牛客小白月赛13 G(双向搜索)
AC通道
两边同步搜,一步里面A走一次B走两次,遇到对方走过的地方就得到了答案。
#include <bits/stdc++.h>
using namespace std;
const int maxn = 1001;
const int tx[] = {-1, 1, 0, 0, -1, -1, 1, 1};
const int ty[] = {0, 0, -1, 1, -1, 1, -1, 1};
int N, M, Ax, Ay, Bx, By;
bool vis[2][maxn][maxn];
char maze[maxn][maxn];
queue<pair<int, int>> Q[2];
bool bfs(int t) {
int control = Q[t].size();
while (control--) {
auto tmp = Q[t].front(); Q[t].pop();
for (int i = 0; i < 8 - 4 * t; i++) {
int x = tmp.first + tx[i];
int y = tmp.second + ty[i];
if (x < 0 || x >= N || y < 0 || y >= M || maze[x][y] == '#')
continue;
if (vis[1 - t][x][y]) return 1;
if (!vis[t][x][y]) Q[t].push({x, y}), vis[t][x][y] = 1;
}
}
return 0;
}
int solve() {
Q[0].push({Ax, Ay});
Q[1].push({Bx, By});
vis[0][Ax][Ay] = 1;
vis[1][Bx][By] = 1;
int step = 0;
while (!Q[0].empty() || !Q[1].empty()) {
step++;
if (bfs(0)) return step;
if (bfs(1)) return step;
if (bfs(1)) return step;
}
return -1;
}
int main() {
scanf("%d %d", &N, &M);
for (int i = 0; i < N; i++) {
for (int j = 0; j < M; j++) {
getchar();
maze[i][j] = getchar();
if (maze[i][j] == 'C') Ax = i, Ay = j;
if (maze[i][j] == 'D') Bx = i, By = j;
}
}
int ans = solve();
if (ans >= 0) printf("YES\n%d\n", ans);
else puts("NO");
return 0;
}