1 专题说明

本专题用来计算使用多源BFS和双端队列BFS求解的题目。

2 训练

题目1：173矩阵距离

C++代码如下，

#include <iostream>
#include <queue>
#include <cstring>using namespace std;const int N = 1010;
int g[N][N];
int d[N][N];
int n, m;int main() {queue<pair<int,int>> q;memset(d, -1, sizeof d);cin >> n >> m;for (int i = 1; i <= n; ++i) {for (int j = 1; j <= m; ++j) {char c;cin >> c;g[i][j] = c - '0';if (g[i][j]) {q.push(make_pair(i,j));d[i][j] = 0;}}}int dirs[4][2] = {{-1,0}, {1,0}, {0,-1}, {0,1}};while (!q.empty()) {auto t = q.front();q.pop();//t下一步可以走到哪里for (int k = 0; k < 4; ++k) {int x = t.first + dirs[k][0];int y = t.second + dirs[k][1];if (x < 1 || x > n || y < 1 || y > m) continue;if (d[x][y] != -1) continue; q.push(make_pair(x,y));d[x][y] = d[t.first][t.second] + 1;}}for (int i = 1; i <= n; ++i) {for (int j = 1; j <= m; ++j) {cout << d[i][j] << " ";}cout << endl;}return 0;
}

题目2：