专题一、简单搜索 - Virtual Judge
很久以前刷完了Virtual Judge上的简单搜索专题，现总结如下：
POJ 1321
由于题目的数据范围比较小，可以直接dfs暴力。读入时记录每个空位的位置，保存在pX[]以及pY[]数组中。暴力的时候统计当前处理第几个空格以及当前处理到了第几行即可。
#include <iostream>
#include <memory.h>
using namespace std;
const int MAX = 128;
long long ans;
int N, K, nCnt;
bool pUsed[MAX];
int pX[MAX], pY[MAX];
int pRow[MAX], pCol[MAX];
void dfs(int x, int y);
int main()
{
char dwTmp;
while(cin >> N >> K)
{
if(N == -1 && K == -1) { break; }
nCnt = 0; ans = 0;
for(int i = 1; i <= N; i++)
{
for(int j = 1; j <= N; j++)
{
cin >> dwTmp;
if(dwTmp == '#')
{ nCnt++; pX[nCnt] = i; pY[nCnt] = j; }
}
cin.ignore();
}
memset(pRow, 0, sizeof(pRow));
memset(pCol, 0, sizeof(pCol));
memset(pUsed, false, sizeof(pUsed));
dfs(1, 0);
cout << ans << endl;
}
return 0;
}
void dfs(int x, int y)
{
if(y == K)
{ ans++; }
else
{
for(int i = x; i <= nCnt; i++)
{
if(!(pUsed[i] || pRow[pX[i]] || pCol[pY[i]]))
{
pRow[pX[i]]++; pCol[pY[i]]++;
pUsed[i] = true;
dfs(i + 1, y + 1);
pUsed[i] = false;
pRow[pX[i]]--; pCol[pY[i]]--;
}
}
}
}
POJ 2251
这是一个三维迷宫，对立体空间的六个方向进行bfs即可。
#include <iostream>
#include <memory.h>
#include <string>
#include <queue>
using namespace std;
const int MAX = 32;
const int dx[] = { 1, -1, 0, 0, 0, 0 };
const int dy[] = { 0, 0, 1, -1, 0, 0 };
const int dz[] = { 0, 0, 0, 0, 1, -1 };
struct Point
{
Point(int _x = 0, int _y = 0, int _z = 0, int _ans = 0)
{ x = _x; y = _y; z = _z; ans = 0; }
int x, y, z, ans;
};
queue<Point> Q;
Point Start, End;
int pMaze[MAX][MAX][MAX];
bool pVisited[MAX][MAX][MAX];
int main()
{
int L, R, C;
string strTmp;
while(cin >> L >> R >> C)
{
if(L == 0 && R == 0 && C == 0) { break; }
while(!Q.empty()) { Q.pop(); }
for(int i = 1; i <= L; i++)
{
for(int j = 1; j <= R; j++)
{
cin >> strTmp;
for(int k = 1; k <= C; k++)
{
if(strTmp[k - 1] == 'S') { pMaze[i][j][k] = 0; Start = Point(i, j, k); }
else if(strTmp[k - 1] == 'E') { pMaze[i][j][k] = 0; End = Point(i, j, k); }
else if(strTmp[k - 1] == '.') { pMaze[i][j][k] = 0; }
else if(strTmp[k - 1] == '#') { pMaze[i][j][k] = 1; }
}
}
}
Q.push(Start);
bool bFlag = false;
memset(pVisited, false, sizeof(pVisited));
pVisited[Start.x][Start.y][Start.z] = true;
while(!Q.empty())
{
Point Now = Q.front(); Q.pop();
if(Now.x == End.x && Now.y == End.y && Now.z == End.z) { cout << "Escaped in " << Now.ans << " minute(s)." << endl; bFlag = true; break; }
for(int i = 0; i < 6; i++)
{
Point Next;
Next.x = Now.x + dx[i]; Next.y = Now.y + dy[i]; Next.z = Now.z + dz[i]; Next.ans = Now.ans + 1;
if(Next.x >= 1 && Next.x <= L && Next.y >= 1 && Next.y <= R && Next.z >= 1 && Next.z <= C &&
pMaze[Next.x][Next.y][Next.z] == 0 && !pVisited[Next.x][Next.y][Next.z])
{
pVisited[Next.x][Next.y][Next.z] = true;
Q.push(Next);
}
}
}
if(!bFlag) { cout << "Trapped!" << endl; }
}
return 0;
}
POJ 3278
同样是bfs，一共三种状态进行转移。
#include <iostream>
#include <memory.h>
#include <queue>
using namespace std;
const int MAX = 1024000;
struct Pos
{
Pos(int _x = 0, int _ans = 0)
{ x = _x; ans = _ans; }
int x, ans;
};
queue<Pos> Q;
bool pVisited[MAX];
int main()
{
int N, K;
while(cin >> N >> K)
{
memset(pVisited, false, sizeof(pVisited));
while(!Q.empty()) { Q.pop(); }
Q.push(Pos(N, 0)); pVisited[N] = true;
while(!Q.empty())
{
Pos Now = Q.front(); Q.pop();
if(Now.x == K) { cout << Now.ans << endl; break; }
if(Now.x * 2 >= 0 && Now.x * 2 < MAX && !pVisited[Now.x * 2])
{
Q.push(Pos(Now.x * 2, Now.ans + 1));
pVisited[Now.x * 2] = true;
}
if(Now.x - 1 >= 0 && Now.x - 1 < MAX && !pVisited[Now.x - 1])
{
Q.push(Pos(Now.x - 1, Now.ans + 1));
pVisited[Now.x - 1] = true;
}
if(Now.x + 1 >= 0 && Now.x + 1 < MAX && !pVisited[Now.x + 1])
{
Q.push(Pos(Now.x + 1, Now.ans + 1));
pVisited[Now.x + 1] = true;
}
}
}
return 0;
}
POJ 3279
考虑到第一行的状态确定以后，后面的N - 1行的状态就确定了，因此只需要枚举第一行，由于数据范围比较小，所以使用二进制状态压缩即可。
#include <iostream>
#include <memory.h>
using namespace std;
const int MAX = 32;
const int dx[] = { 1, -1, 0, 0 };
const int dy[] = { 0, 0, 1, -1 };
int M, N;
int pMap[MAX][MAX];
int pAns[MAX][MAX], pTmp[MAX][MAX];
int Solve();
int IsFlip(int x, int y);
int main()
{
while(cin >> M >> N)
{
int ans = 2147483647;
for(int i = 1; i <= M; i++)
{
for(int j = 1; j <= N; j++)
{ cin >> pMap[i][j]; }
}
for(int i = 0; i < (1 << N); i++)
{
memset(pTmp, 0, sizeof(pTmp));
for(int j = 1; j <= N; j++)
{
if(i & (1 << j - 1))
{ pTmp[1][j] = 1; }
}
int nTmp = Solve();
if(nTmp == -1) { continue; }
if(nTmp < ans)
{
ans = nTmp;
memcpy(pAns, pTmp, sizeof(pTmp));
}
}
if(ans != 2147483647)
{
for(int i = 1; i <= M; i++)
{
for(int j = 1; j <= N; j++)
{
cout << pAns[i][j];
if(j != N) { cout << " "; }
}
cout << endl;
}
}
else { cout << "IMPOSSIBLE" << endl; }
}
return 0;
}
int Solve()
{
int nRet = 0;
for(int i = 2; i <= M; i++)
{
for(int j = 1; j <= N; j++)
{
if(IsFlip(i - 1, j)) { pTmp[i][j] = 1; }
}
}
for(int i = 1; i <= N; i++)
{
if(IsFlip(M, i)) { return -1; }
}
for(int i = 1; i <= M; i++)
{
for(int j = 1; j <= N; j++)
{
nRet += pTmp[i][j];
}
}
return nRet;
}
int IsFlip(int x, int y)
{
int nRet = pTmp[x][y];
for(int i = 0; i < 4; i++)
{
int nx = x + dx[i];
int ny = y + dy[i];
if(nx >= 1 && nx <= M && ny >= 1 && ny <= N)
{ nRet += pTmp[nx][ny]; }
}
nRet += pMap[x][y];
return nRet & 1;
}
POJ 1426
这道题目也是一道bfs，只需要记录每次遍历到的结果tmp % N，同时保存已选取的数字的内容，最后判断已选取的数字的长度是否符合题目的要求。
#include <iostream>
#include <memory.h>
#include <string>
#include <queue>
using namespace std;
const int MAX = 256;
const int d[] = { 0, 1 };
struct Num
{
Num(int _nNum = 1, string _ans = "1")
{
nNum = _nNum;
ans = _ans;
}
int nNum;
string ans;
};
int N;
bool pVisited[MAX];
queue<Num> Q;
int main()
{
while(cin >> N)
{
if(N == 0) { break; }
else
{
while(!Q.empty()) { Q.pop(); }
memset(pVisited, false, sizeof(pVisited));
Q.push(Num(1)); pVisited[1 % N] = true;
while(!Q.empty())
{
Num Now = Q.front(); Q.pop();
if(Now.nNum % N == 0) { cout << Now.ans << endl; break; }
for(int i = 0; i < 2; i++)
{
Num Next = Now;
if(!pVisited[(Now.nNum * 10 + d[i]) % N])
{
pVisited[(Now.nNum * 10 + d[i]) % N] = true;
Q.push(Num((Now.nNum * 10 + d[i]) % N, Now.ans + (char)(d[i] + '0')));
}
}
}
}
}
return 0;
}
POJ 3126
bfs水题。
#include <iostream>
#include <memory.h>
#include <string>
#include <queue>
#include <set>
using namespace std;
const int MAX = 10240;
struct Prime
{
Prime(int _x = 0, int _ans = 0)
{ x = _x; ans = _ans; }
int x, ans;
};
set<int> S;
queue<Prime> Q;
bool pVisited[MAX];
int Change(int x, int y, int z);
int main()
{
for(int i = 1000; i <= 9999; i++)
{
bool bFlag = true;
for(int j = 2; j * j <= i; j++)
{
if(i % j == 0) { bFlag = false; }
}
if(bFlag) { S.insert(i); }
}
int N, s, e;
while(cin >> N)
{
for(int i = 1; i <= N; i++)
{
while(!Q.empty()) { Q.pop(); }
memset(pVisited, false, sizeof(pVisited));
cin >> s >> e;
Q.push(Prime(s, 0)); pVisited[s] = true;
while(!Q.empty())
{
Prime Now = Q.front(); Q.pop();
if(Now.x == e) { cout << Now.ans << endl; break; }
for(int i = 0; i < 4; i++)
{
for(int j = 0; j <= 9; j++)
{
int nNext = Change(Now.x, i, j);
if(S.count(nNext) && !pVisited[nNext])
{
Q.push(Prime(nNext, Now.ans + 1));
pVisited[nNext] = true;
}
}
}
}
}
}
return 0;
}
int Change(int x, int y, int z)
{
int nTmp = 1;
while(y--) { nTmp *= 10; }
x -= x / nTmp % 10 * nTmp;
x += z * nTmp;
return x;
}
POJ 3087
模拟整个过程即可，如果出现与初始情况相同的情形，就说明无解。
#include <iostream>
#include <string>
using namespace std;
int main()
{
int N, C;
bool bFlag;
string SA, SB, S, Init;
cin >> N;
for(int i = 1; i <= N; i++)
{
cin >> C >> SA >> SB >> S;
int nCnt = 0; Init = ""; bFlag = false;
while(1)
{
nCnt++;
string ans = "";
for(int j = 0; j < SA.size(); j++)
{
ans += SB[j];
ans += SA[j];
}
if(Init == "") { Init = ans; }
SA = ans.substr(0, C);
SB = ans.substr(C, C);
if(nCnt != 1 && ans == Init) { break; }
if(ans == S) { cout << i << " " << nCnt << endl; bFlag = true; break; }
}
if(!bFlag) { cout << i << " -1" << endl; }
}
return 0;
}
POJ 3414
bfs水题。处理好倒水的过程即可。
#include <iostream>
#include <memory.h>
#include <string>
#include <queue>
using namespace std;
const int MAX = 128;
struct Pots
{
Pots(int _A = 0, int _B = 0)
{
A = _A; B = _B;
while(!pOpt.empty()) { pOpt.pop(); }
}
int A, B;
queue<string> pOpt;
};
int A, B, C;
bool pVisited[MAX][MAX];
queue<Pots> Q;
Pots Opt(Pots Now, int k);
Pots Fill(Pots Now, int x);
Pots Drop(Pots Now, int x);
Pots Pour(Pots Now, int x);
int main()
{
bool bFlag;
while(cin >> A >> B >> C)
{
bFlag = false;
while(!Q.empty()) { Q.empty(); }
memset(pVisited, false, sizeof(pVisited));
Q.push(Pots(0, 0)); pVisited[0][0] = true;
while(!Q.empty())
{
Pots Now = Q.front(); Q.pop();
if(Now.A == C || Now.B == C)
{
cout << Now.pOpt.size() << endl;
while(!Now.pOpt.empty())
{
cout << Now.pOpt.front() << endl;
Now.pOpt.pop();
}
bFlag = true;
break;
}
for(int i = 0; i < 6; i++)
{
Pots Next = Opt(Now, i);
if(!pVisited[Next.A][Next.B])
{
Q.push(Next);
pVisited[Next.A][Next.B] = true;
}
}
}
if(!bFlag) { cout << "impossible" << endl; }
}
return 0;
}
Pots Opt(Pots Now, int k)
{
switch(k)
{
case 0:
return Fill(Now, 0);
case 1:
return Fill(Now, 1);
case 2:
return Drop(Now, 0);
case 3:
return Drop(Now, 1);
case 4:
return Pour(Now, 0);
case 5:
return Pour(Now, 1);
}
}
Pots Fill(Pots Now, int x)
{
if(x == 0) { Now.A = A; Now.pOpt.push("FILL(1)"); }
else { Now.B = B; Now.pOpt.push("FILL(2)"); }
return Now;
}
Pots Drop(Pots Now, int x)
{
if(x == 0) { Now.A = 0; Now.pOpt.push("DROP(1)"); }
else { Now.B = 0; Now.pOpt.push("DROP(2)"); }
return Now;
}
Pots Pour(Pots Now, int x)
{
if(x == 0)
{
Now.B += Now.A;
if(Now.B > B) { Now.A = Now.B - B; Now.B = B; }
else { Now.A = 0; }
Now.pOpt.push("POUR(1,2)");
}
else
{
Now.A += Now.B;
if(Now.A > A) { Now.B = Now.A - A; Now.A = A; }
else { Now.B = 0; }
Now.pOpt.push("POUR(2,1)");
}
return Now;
}
FZU 2150
暴力枚举两个起点，然后bfs。
#include <iostream>
#include <memory.h>
#include <string>
#include <queue>
using namespace std;
const int MAX = 16;
const int dx[] = { 1, -1, 0, 0 };
const int dy[] = { 0, 0, 1, -1 };
struct Pos
{
Pos(int _x, int _y, int _ans)
{ x = _x; y = _y; ans = _ans; }
int x, y, ans;
};
int T, N, M;
int pMap[MAX][MAX];
bool pVisited[MAX][MAX];
queue<Pos> Q;
bool Check();
int Bfs(Pos A, Pos B);
int main()
{
string strTmp;
cin >> T;
for(int k = 1; k <= T; k++)
{
cin >> N >> M;
int ans = 2147483647;
bool bFlag = false;
for(int i = 1; i <= N; i++)
{
cin >> strTmp;
for(int j = 1; j <= M; j++)
{
if(strTmp[j - 1] == '.') { pMap[i][j] = 1; }
else { pMap[i][j] = 0; }
}
}
for(int i = 1; i <= N; i++)
{
for(int j = 1; j <= M; j++)
{
for(int p = 1; p <= N; p++)
{
for(int q = 1; q <= M; q++)
{
if(pMap[i][j] || pMap[p][q]) { continue; }
int nTmp = Bfs(Pos(i, j, 0), Pos(p, q, 0));
if(Check()) { ans = min(ans, nTmp); bFlag = true; }
}
}
}
}
cout << "Case " << k << ": ";
if(bFlag) { cout << ans << endl; }
else { cout << -1 << endl; }
}
return 0;
}
int Bfs(Pos A, Pos B)
{
int nRet = 0;
while(!Q.empty()) { Q.pop(); }
memset(pVisited, false, sizeof(pVisited));
Q.push(A); pVisited[A.x][A.y] = true;
Q.push(B); pVisited[B.x][B.y] = true;
while(!Q.empty())
{
Pos Now = Q.front(); Q.pop();
nRet = max(nRet, Now.ans);
for(int i = 0; i < 4; i++)
{
Pos Next = Now; Next.ans++;
Next.x += dx[i]; Next.y += dy[i];
if(Next.x >= 1 && Next.x <= N &&
Next.y >= 1 && Next.y <= M &&
!pVisited[Next.x][Next.y] && !pMap[Next.x][Next.y])
{
Q.push(Next);
pVisited[Next.x][Next.y] = true;
}
}
}
return nRet;
}
bool Check()
{
for(int i = 1; i <= N; i++)
{
for(int j = 1; j <= M; j++)
{
if(!pMap[i][j] && !pVisited[i][j])
{ return false; }
}
}
return true;
}
UVa 11624
注意可能有多个点起火，设定一个全局时间量，用来控制人以及火的运动顺序，先处理火，再处理人。然后就是bfs水题。
#include <iostream>
#include <memory.h>
#include <queue>
using namespace std;
const int MAX = 1024;
const int dx[] = { 1, -1, 0, 0 };
const int dy[] = { 0, 0, 1, -1 };
struct Pos
{
Pos(int _x = 0, int _y = 0, int _ans = 0)
{ x = _x; y = _y; ans = _ans; }
int x, y, ans;
};
int T, R, C;
int pMap[MAX][MAX];
bool pVJ[MAX][MAX], pVF[MAX][MAX];
queue<Pos> J, F;
int main()
{
string strTmp;
cin >> T;
for(int k = 1; k <= T; k++)
{
cin >> R >> C;
bool bFlag = false;
while(!J.empty()) { J.pop(); }
while(!F.empty()) { F.pop(); }
memset(pVJ, false, sizeof(pVJ));
memset(pVF, false, sizeof(pVF));
for(int i = 1; i <= R; i++)
{
cin >> strTmp;
for(int j = 1; j <= C; j++)
{
if(strTmp[j - 1] == '#') { pMap[i][j] = 1; }
else { pMap[i][j] = 0; }
if(strTmp[j - 1] == 'J') { J.push(Pos(i, j)); pVJ[i][j] = true; }
if(strTmp[j - 1] == 'F') { F.push(Pos(i, j)); pVF[i][j] = true; }
}
}
int nTime = 0;
while(!J.empty())
{
while(!F.empty() && F.front().ans <= nTime)
{
Pos FN = F.front(); F.pop();
for(int i = 0; i < 4; i++)
{
Pos Next = FN; Next.ans++;
Next.x += dx[i]; Next.y += dy[i];
if(Next.x >= 1 && Next.x <= R && Next.y >= 1 && Next.y <= C &&
!pMap[Next.x][Next.y] && !pVF[Next.x][Next.y])
{
F.push(Next);
pVF[Next.x][Next.y] = true;
}
}
}
while(!J.empty() && J.front().ans <= nTime)
{
Pos JN = J.front(); J.pop();
if(JN.x == 1 || JN.x == R || JN.y == 1 || JN.y == C) { cout << JN.ans + 1 << endl; bFlag = true; break; }
for(int i = 0; i < 4; i++)
{
Pos Next = JN; Next.ans++;
Next.x += dx[i]; Next.y += dy[i];
if(Next.x >= 1 && Next.x <= R && Next.y >= 1 && Next.y <= C &&
!pMap[Next.x][Next.y] && !pVF[Next.x][Next.y] && !pVJ[Next.x][Next.y])
{
J.push(Next);
pVJ[Next.x][Next.y] = true;
}
}
}
if(bFlag) { break; }
nTime++;
}
if(!bFlag) { cout << "IMPOSSIBLE" << endl; }
}
return 0;
}
POJ 3984
bfs水题。
#include <iostream>
#include <memory.h>
#include <queue>
using namespace std;
const int MAX = 8;
const int dx[] = { 1, -1, 0, 0 };
const int dy[] = { 0, 0, 1, -1 };
struct Pos
{
Pos(int _x = 0, int _y = 0)
{ x = _x; y = _y; }
int x, y;
};
struct State
{
State(int _x = 0, int _y = 0)
{
Now = Pos(_x, _y);
while(!Ans.empty()) { Ans.pop(); }
}
Pos Now;
queue<Pos> Ans;
};
int pMap[MAX][MAX];
bool pVisited[MAX][MAX];
queue<State> Q;
int main()
{
for(int i = 1; i <= 5; i++)
{
for(int j = 1; j <= 5; j++)
{ cin >> pMap[i][j]; }
}
while(!Q.empty()) { Q.pop(); }
memset(pVisited, false, sizeof(pVisited));
Q.push(State(1, 1)); pVisited[1][1] = true;
while(!Q.empty())
{
State Now = Q.front(); Q.pop();
if(Now.Now.x == 5 && Now.Now.y == 5)
{
while(!Now.Ans.empty())
{
Pos Cur = Now.Ans.front();
cout << "(" << Cur.x - 1 << ", " << Cur.y - 1 << ")" << endl;
Now.Ans.pop();
}
cout << "(4, 4)" << endl;
break;
}
for(int i = 0; i < 4; i++)
{
int nx = Now.Now.x + dx[i];
int ny = Now.Now.y + dy[i];
if(nx >= 1 && nx <= 5 && ny >= 1 && ny <= 5 &&
!pVisited[nx][ny] && !pMap[nx][ny])
{
State Next = Now;
Next.Now = Pos(nx, ny);
Next.Ans.push(Now.Now);
Q.push(Next);
pVisited[nx][ny] = true;
}
}
}
return 0;
}
HDU 1241
求连通块个数，直接dfs即可。
#include <iostream>
#include <memory.h>
#include <string>
#include <queue>
using namespace std;
const int MAX = 128;
const int dx[] = { -1, 0, 1, -1, 1, -1, 0, 1 };
const int dy[] = { 1, 1, 1, 0, 0, -1, -1, -1 };
int N, M;
int pMap[MAX][MAX];
bool pVisited[MAX][MAX];
void dfs(int x, int y);
int main()
{
string strTmp;
while(cin >> N >> M)
{
if(N == 0 && M == 0) { break; }
for(int i = 1; i <= N; i++)
{
cin >> strTmp;
for(int j = 1; j <= M; j++)
{
if(strTmp[j - 1] == '*') { pMap[i][j] = 1; }
else { pMap[i][j] = 0; }
}
}
int ans = 0;
memset(pVisited, false, sizeof(pVisited));
for(int i = 1; i <= N; i++)
{
for(int j = 1; j <= M; j++)
{
if(!pMap[i][j] && !pVisited[i][j])
{
dfs(i, j);
ans++;
}
}
}
cout << ans << endl;
}
return 0;
}
void dfs(int x, int y)
{
pVisited[x][y] = true;
for(int i = 0; i < 8; i++)
{
int nx = x + dx[i];
int ny = y + dy[i];
if(nx >= 1 && nx <= N && ny >= 1 && ny <= M &&
!pMap[nx][ny] && !pVisited[nx][ny])
{ dfs(nx, ny); }
}
}
HDU 1495
这道题目和POJ 3414非常的类似，但相较来说更简单，也是一道bfs水题。
#include <iostream>
#include <memory.h>
#include <queue>
using namespace std;
const int MAX = 128;
struct Cola
{
Cola(int _S = 0, int _N = 0, int _M = 0, int _ans = 0)
{ S = _S; N = _N; M = _M; ans = _ans; }
int S, N, M, ans;
};
int S, N, M;
bool pVisited[MAX][MAX][MAX];
queue<Cola> Q;
Cola Opt(Cola Now, int k);
bool Check(Cola Now);
int main()
{
while(cin >> S >> N >> M)
{
if(S == 0 && N == 0 && M == 0) { break; }
if(S & 1) { cout << "NO" << endl; }
else
{
bool bFlag = false;
memset(pVisited, false, sizeof(pVisited));
while(!Q.empty()) { Q.pop(); } // 队列忘记清空
Q.push(Cola(S, 0, 0, 0)); pVisited[S][0][0] = true;
while(!Q.empty())
{
Cola Now = Q.front(); Q.pop();
if(Check(Now))
{
cout << Now.ans << endl;
bFlag = true;
break;
}
for(int i = 0; i < 6; i++)
{
Cola Next = Opt(Now, i);
if(!pVisited[Next.S][Next.N][Next.M])
{
Q.push(Cola(Next.S, Next.N, Next.M, Next.ans));
pVisited[Next.S][Next.N][Next.M] = true;
}
}
}
if(!bFlag) { cout << "NO" << endl; }
}
}
return 0;
}
Cola Opt(Cola Now, int k)
{
if(k == 0)
{
Now.N += Now.S;
if(Now.N > N) { Now.S = Now.N - N; Now.N = N; }
else { Now.S = 0; }
}
if(k == 1)
{
Now.S += Now.N;
Now.N = 0;
}
if(k == 2)
{
Now.M += Now.S;
if(Now.M > M) { Now.S = Now.M - M; Now.M = M; }
else { Now.S = 0; }
}
if(k == 3)
{
Now.S += Now.M;
Now.M = 0;
}
if(k == 4)
{
Now.N += Now.M;
if(Now.N > N) { Now.M = Now.N - N; Now.N = N; }
else { Now.M = 0; }
}
if(k == 5)
{
Now.M += Now.N;
if(Now.M > M) { Now.N = Now.M - M; Now.M = M; }
else { Now.N = 0; }
}
Now.ans++;
return Now;
}
bool Check(Cola Now)
{
int x = Now.S, y = Now.N, z = Now.M, p = S / 2;
return (x == p && y == p) || (x == p && z == p) || (y == p && z == p);
}
HDU 2612
首先计算Y和M走到地图上每个点的最小时间，然后枚举每个点，计算Y和M走到该点时间和的最小值，最后结果乘以11分钟即可。
#include <iostream>
#include <memory.h>
#include <string>
#include <queue>
using namespace std;
const int MAX = 256;
const int dx[] = { 1, -1, 0, 0 };
const int dy[] = { 0, 0, 1, -1 };
struct Pos
{
Pos(int _x = 0, int _y = 0, int _s = 0)
{ x = _x; y = _y; s = _s; }
int x, y, s;
};
Pos SY, SM;
int N, M;
int pMap[MAX][MAX];
int pAns[2][MAX][MAX];
bool pVisited[MAX][MAX];
queue<Pos> Q;
void Solve(Pos S, int k);
int main()
{
string strTmp;
while(cin >> N >> M)
{
memset(pAns, -1, sizeof(pAns));
for(int i = 1; i <= N; i++)
{
cin >> strTmp;
for(int j = 1; j <= M; j++)
{
if(strTmp[j - 1] == '#') { pMap[i][j] = 1; }
else if(strTmp[j - 1] == '@') { pMap[i][j] = 2; }
else { pMap[i][j] = 0; }
if(strTmp[j - 1] == 'Y') { SY = Pos(i, j, 0); }
if(strTmp[j - 1] == 'M') { SM = Pos(i, j, 0); }
}
}
Solve(SY, 0); Solve(SM, 1);
int ans = 2147483647;
for(int i = 1; i <= N; i++)
{
for(int j = 1; j <= M; j++)
{
if(pMap[i][j] == 2 && pAns[0][i][j] != -1 && pAns[1][i][j] != -1)
{ ans = min(ans, pAns[0][i][j] + pAns[1][i][j]); }
}
}
cout << ans * 11 << endl;
}
return 0;
}
void Solve(Pos S, int k)
{
while(!Q.empty()) { Q.pop(); }
memset(pVisited, false, sizeof(pVisited));
Q.push(S); pVisited[S.x][S.y] = true;
while(!Q.empty())
{
Pos Now = Q.front(); Q.pop();
if(pAns[k][Now.x][Now.y] == -1)
{ pAns[k][Now.x][Now.y] = Now.s; }
for(int i = 0; i < 4; i++)
{
int nx = Now.x + dx[i];
int ny = Now.y + dy[i];
if(nx >= 1 && nx <= N && ny >= 1 && ny <= M &&
!pVisited[nx][ny] && pMap[nx][ny] != 1)
{
Q.push(Pos(nx, ny, Now.s + 1));
pVisited[nx][ny] = true;
}
}
}
}
刷完这个专题，感觉对bfs的理解更加深入透彻了。
