POJ 1463 Strategic game（二分图最大匹配）

Description

Bob enjoys playing computer games, especially strategic games, but sometimes he cannot find the solution fast enough and then he is very sad. Now he has the following problem. He must defend a medieval city, the roads of which form a tree. He has to put the minimum number of soldiers on the nodes so that they can observe all the edges. Can you help him?
Your program should find the minimum number of soldiers that Bob has to put for a given tree.
For example for the tree:

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

const int MAXN = 1510;
const int MAXE = MAXN << 1;

int head[MAXN];
int to[MAXE], next[MAXE];
int n, ecnt;

void init() {
memset(head, 0, sizeof(head));
ecnt = 2;
}

void add_edge(int u, int v) {
to[ecnt] = v; next[ecnt] = head[u]; head[u] = ecnt++;
to[ecnt] = u; next[ecnt] = head[v]; head[v] = ecnt++;
}

int link[MAXN], dep[MAXN];
bool vis[MAXN];

bool dfs(int u) {
for(int p = head[u]; p; p = next[p]) {
int &v = to[p];
if(vis[v]) continue;
vis[v] = true;
if(!~link[v] || dfs(link[v])) {
link[v] = u;
return true;
}
}
return false;
}

int main() {
while(scanf("%d", &n) != EOF) {
init();
memset(dep, 0, sizeof(dep));
for(int i = 0; i < n; ++i) {
int a, b, c;
scanf("%d:(%d)", &a, &b);
while(b--) {
scanf("%d", &c);
dep[c] = dep[a] + 1;
add_edge(a, c);
}
}
int ans = 0;
memset(link, 255, sizeof(link));
for(int i = 0; i < n; ++i) {
if(dep[i] & 1) continue;
memset(vis, 0, sizeof(vis));
if(dfs(i)) ++ans;
}
printf("%d\n", ans);
}
}

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