【HDOJ】2444 The Accomodation of Students

图论的题目。着色原理+二分图匹配。

#include <cstdio>
#include <cstring>

#define MAXN 205

char map[MAXN][MAXN];
int link[MAXN];
int color[MAXN];
bool visit[MAXN];
int n, m;

bool dfs(int v, int col) {
    int i;

    for (i=1; i<=n; ++i) {
        if (map[i][v]) {
            if (color[i] == col)
                return false;
            else if (color[i] == 0) {
                color[i] = -col;
                if (dfs(i, -col) == false)
                    return false;
            }
        }
    }
    return true;
}

bool find(int v) {
    int i;

    for (i=1; i<=n; ++i) {
        if (!visit[i] && map[i][v]) {
            visit[i] = true;
            if (link[i]==0 || find(link[i])) {
                link[i] = v;
                return true;
            }
        }
    }
    return false;
}

int main() {
    int ans;
    int i, j;

    while (scanf("%d%d", &n, &m) != EOF) {
        memset(map, 0, sizeof(map));
        memset(link, 0, sizeof(link));
        memset(color, 0, sizeof(color));
        while (m--) {
            scanf("%d %d", &i, &j);
            map[i][j] = map[j][i] = 1;
        }
        color[1] = 1;
        if (dfs(1, 1) == false) {
            printf("No\n");
            continue;
        }
        for (ans=0, i=1; i<=n; ++i) {
            memset(visit, false, sizeof(visit));
            if (find(i))
                ++ans;
        }
        printf("%d\n", ans/2);
    }

    return 0;
}