POJ - 3469 -- Dual Core CPU

题目来源：http://poj.org/problem?id=3469

由于maxm开小了，RE了好多发。另外，G++交的TLE了，用C++过的。

最小割问题，由定理知，最小割=最大流，因此可用最大流Dinic算法解决。

代码：

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <queue>
using namespace std;
const int maxn=2e4+10;
const int maxm=2e6+10;
struct edge{
    int to,next,cap,rev;
}e[maxm];
int n,m,cnt=0,head[maxn],dis[maxn],iter[maxn];
queue<int> q;
void ins(int x,int y,int z) {
    e[++cnt].to = y;
    e[cnt].next = head[x];
    head[x] = cnt;
    e[cnt].cap = z;
    e[cnt].rev = cnt + 1;
    e[++cnt].to = x;
    e[cnt].next = head[y];
    head[y] = cnt;
    e[cnt].cap = 0;
    e[cnt].rev = cnt - 1;
}
void bfs(int s) {
    memset(dis, -1, sizeof(dis));
    while (!q.empty())q.pop();
    dis[s] = 0;
    q.push(s);
    while (!q.empty()) {
        int u = q.front();
        q.pop();
        for (int i = head[u]; i; i = e[i].next) {
            if (e[i].cap && dis[e[i].to] < 0) {
                q.push(e[i].to);
                dis[e[i].to] = dis[u] + 1;
            }
        }
    }
}
int dfs(int v,int t,int f) {
    if (v == t)return f;
    for (int i = (iter[v] ? iter[v] : head[v]); i; i = e[i].next, iter[v] = i) {
        if (e[i].cap && dis[v] < dis[e[i].to]) {
            int d = dfs(e[i].to, t, min(f, e[i].cap));
            if (d > 0) {
                e[i].cap -= d;
                e[e[i].rev].cap += d;
                return d;
            }
        }
    }
    return 0;
}
int max_flow(int s,int t) {
    int flow = 0;
    for (;;) {
        bfs(s);
        if (dis[t] < 0)return flow;
        memset(iter, 0, sizeof(iter));
        int f;
        while ((f = dfs(s, t, 1e9)) > 0)
            flow += f;
    }
}
int main() {
    while (~scanf("%d%d", &n, &m)) {
        memset(head, 0, sizeof(head));
        cnt = 0;
        int s = n + 1, t = n + 2;
        for (int i = 1; i <= n; ++i) {
            int x, y;
            scanf("%d%d", &x, &y);
            ins(s, i, x);
            ins(i, t, y);
        }
        for (int i = 1; i <= m; ++i) {
            int x, y, z;
            scanf("%d%d%d", &x, &y, &z);
            ins(x, y, z);
            ins(y, x, z);
        }
        printf("%d\n", max_flow(s, t));
    }
    return 0;
}