AcWing 377. 泥泞的区域

算法

二分图+最小点覆盖

思路

详见《进阶指南》

代码

#include <cstdio>
#include <vector>
#include <cstring>
#include <iostream>
using namespace std;
const int N = 56;
int n, m, tot = 1, a[N][N][2], f[N*N], ans;
char s[N][N];
bool v[N*N];
vector<int> e[N*N];

bool dfs(int x) {
    for (unsigned int i = 0; i < e[x].size(); i++) {
        int y = e[x][i];
        if (v[y]) continue;
        v[y] = 1;
        if (!f[y] || dfs(f[y])) {
            f[y] = x;
            return 1;
        }
    }
    return 0;
}

int main() {
    cin >> n >> m;
    for (int i = 1; i <= n; i++) scanf("%s", s[i] + 1);
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m + 1; j++)
            if (s[i][j] == '*') a[i][j][0] = tot;
            else ++tot;
    int t = tot;
    for (int j = 1; j <= m; j++)
        for (int i = 1; i <= n + 1; i++)
            if (s[i][j] == '*') a[i][j][1] = tot;
            else ++tot;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            if (s[i][j] == '*') {
                e[a[i][j][0]].push_back(a[i][j][1]);
                e[a[i][j][1]].push_back(a[i][j][0]);
            }
    for (int i = 1; i < t; i++) {
        memset(v, 0, sizeof(v));
        ans += dfs(i);
    }
    cout << ans << endl;
    return 0;
}

作者：ruanmowen
链接：https://www.acwing.com/activity/content/code/content/278239/
来源：AcWing
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