UVA 11748 - Rigging Elections（dfs)

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UVA 11748 - Rigging Elections

题目链接

题意：n个人选举，给出m个人的投票人对于每个人的优先级，现在你想让第c个人赢，问能不能

思路：对于两个人上场，如果a能赢b,就建一条a->b的边，然后问题其实就变成能否以c为根节点是一棵树，直接dfs一遍即可

代码：

#include <cstdio>#include <cstring>#include <vector>using namespace std;const int N = 105;int n, m, c, a[N][N], vis[N];vector<int> g[N];int dfs(int u) {vis[u] = 1;int ans = 1;for (int i = 0; i < g[u].size(); i++) if (!vis[g[u][i]])ans += dfs(g[u][i]);return ans;}int main() {while (~scanf("%d%d%d", &n, &m, &c) && n) {int u;for (int i = 1; i <= n; i++)g[i].clear();for (int i = 1; i <= m; i++)for (int j = 1; j <= n; j++) {scanf("%d", &u);a[i][u] = j;}for (int i = 1; i <= n; i++) {for (int j = i + 1; j <= n; j++) {int cnt = 0;for (int k = 1; k <= m; k++) {if (a[k][i] < a[k][j])cnt++;if (cnt > m / 2) break;}if (cnt > m / 2) g[i].push_back(j);else g[j].push_back(i);}}memset(vis, 0, sizeof(vis));printf("%s\n", dfs(c) == n ? "yes" : "no");}return 0;}

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