[BFS模板题] 数组版/STL版 以及记录路线

目录

题目 

​

 用数组模拟队列

运用queue

拓展:记录路线

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题目 

 输入样例：

5 5
0 1 0 0 0
0 1 0 1 0
0 0 0 0 0
0 1 1 1 0
0 0 0 1 0

输出样例：

8

 用数组模拟队列

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;

const int N = 110;

typedef pair<int, int> PII;
PII q[N*N];
int n,m;
int g[N][N],step[N][N];

int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};

int bfs()
{
    memset(step, -1, sizeof step);
    
    int x = 0, y = 0;
    q[0] = {0, 0};
    step[0][0] = 0;
    
    while(x <= y)
    {
        auto t = q[x++];
        for(int i = 0; i < 4; i ++)
        {
            int nx = t.first + dx[i], ny = t.second + dy[i];
            if(nx>=0 && ny>=0 && nx<n && ny<m && !g[nx][ny] && step[nx][ny]==-1){
                step[nx][ny] = step[t.first][t.second] + 1;
                q[++y] = {nx, ny};
            }
        }
    }
    return step[n-1][m-1];
}
int main()
{
    cin >> n >> m;
    for (int i = 0; i < n; i ++ )
        for (int j = 0; j < m; j ++ )
            scanf("%d", &g[i][j]);
    cout << bfs() << endl;
    return 0;
}

运用queue

#include <iostream>
#include <cstring>
#include <algorithm>
#include <queue>

using namespace std;

const int N = 110;

typedef pair<int, int> PII;
queue<PII> q;
int n,m;
int g[N][N],step[N][N];

int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};

int bfs()
{
    memset(step, -1, sizeof step);
    
    int x = 0, y = 0;
    q.push({0, 0});
    step[0][0] = 0;
    
    while(!q.empty())
    {
        auto t = q.front();
        q.pop();
        
        for(int i = 0; i < 4; i ++)
        {
            int nx = t.first + dx[i], ny = t.second + dy[i];
            if(nx>=0 && ny>=0 && nx<n && ny<m && !g[nx][ny] && step[nx][ny]==-1){
                step[nx][ny] = step[t.first][t.second] + 1;
                q.push({nx, ny});
            }
        }
    }
    return step[n-1][m-1];
}
int main()
{
    cin >> n >> m;
    for (int i = 0; i < n; i ++ )
        for (int j = 0; j < m; j ++ )
            scanf("%d", &g[i][j]);
    cout << bfs() << endl;
    return 0;
}

拓展:记录路线

只需要新增加一个数对数组pre用来回忆即可

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;

const int N = 110;

typedef pair<int, int> PII;
PII q[N*N],pre[N][N];
int n,m;
int g[N][N],step[N][N];

int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};

int bfs()
{
    memset(step, -1, sizeof step);
    
    int x = 0, y = 0;
    q[0] = {0, 0};
    step[0][0] = 0;
    
    while(x <= y)
    {
        auto t = q[x++];
        for(int i = 0; i < 4; i ++)
        {
            int nx = t.first + dx[i], ny = t.second + dy[i];
            if(nx>=0 && ny>=0 && nx<n && ny<m && !g[nx][ny] && step[nx][ny]==-1){
                step[nx][ny] = step[t.first][t.second] + 1;
                pre[nx][ny] = {t.first, t.second};
                q[++y] = {nx, ny};
            }
        }
    }
    
    x = n-1, y = m-1;
    
    while(x || y)
    {
        cout << x << ' ' << y << endl;
        auto t = pre[x][y];
        x = t.first, y = t.second;
    }
    return step[n-1][m-1];
}
int main()
{
    cin >> n >> m;
    for (int i = 0; i < n; i ++ )
        for (int j = 0; j < m; j ++ )
            scanf("%d", &g[i][j]);
    cout << bfs() << endl;
    return 0;
}

效果