wenbao与差分约束

推荐博客：http://www.cppblog.com/menjitianya/archive/2015/11/19/212292.html

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http://poj.org/problem?id=3169

#include "iostream"
#include <string.h>
#include <stdio.h>
using namespace std;

#define INF 1e9
const int maxn = 10009*2;
int n, ml, md, index, m;
int head[maxn], to[maxn], pre[maxn], w[maxn], queue[maxn], dis[maxn], cnt[maxn];

void init() {
    index = 1;
    for(int i = 1; i <= n; ++i) head[i] = 0, cnt[i] = 0;
}

void add(int x, int y, int z) {
    to[index] = y;
    w[index] = z;
    pre[index] = head[x];
    head[x] = index++;
}

bool mark[maxn];

int spfa() {
    int front = 0, rear = 0;
    for(int i = 1; i <= n; ++i) {
        dis[i] = INF;
        add(i, i-1, 0);
    }
    dis[1] = 0;
    queue[rear++] = 1;
    while(front != rear) {
        int k = queue[front++];
        mark[k] = false;
        for(int i = head[k]; i; i = pre[i]){
            if(dis[k] + w[i] < dis[to[i]]) {
                dis[to[i]] = dis[k] + w[i];
                if(!mark[to[i]]) {
                    if(++cnt[to[i]] > n) return -1;
                    queue[rear++] = to[i];
                    mark[to[i]] = true;
                }
            }
        }
    }
    if(dis[n] == INF) return -2;
    return dis[n];
}

int main() {
#ifdef wenbao
    freopen("in", "r", stdin);
#endif
    while(~scanf("%d%d%d", &n, &ml, &md)) {
        init();
        int x, y, z;
        for(int i = 0; i < ml; ++i) {
            scanf("%d%d%d", &x, &y, &z);
            add(x, y, z);
        }
        for(int i = 0; i < md; ++i) {
            scanf("%d%d%d", &x, &y, &z);
            add(y, x, -z);
        }
        printf("%d
", spfa());
    }
    return 0;
}

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