POJ 2983 Is the Information Reliable? 差分约束

题目：http://poj.org/problem?id=2983

#include <stdio.h>
#include <string.h>

struct Edge
{
    int u, v, w;
}edge[200010];

int main()
{
    int n, m;
    int dist[1010];
    int u, v, w;
    char s[2];
    while(scanf("%d %d", &n, &m) != EOF)
    {
        memset(dist, 0, sizeof(dist));
        int cnt = 0;
        for(int i = 0; i < m; i++)
        {
            scanf("%s", s);
            if(s[0] == 'P')
            {
                scanf("%d %d %d", &u, &v, &w);
                edge[cnt].u = u;
                edge[cnt].v = v;
                edge[cnt++].w = w;

                edge[cnt].u = v;
                edge[cnt].v = u;
                edge[cnt++].w = -w;
            }
            else
            {
                scanf("%d %d", &u, &v);
                edge[cnt].u = u;
                edge[cnt].v = v;
                edge[cnt++].w = 1;
            }
        }

        for(int i = 0; i < n; i++)
        {
            for(int j = 0; j < cnt; j++)
            {
                if(dist[edge[j].v] > dist[edge[j].u] - edge[j].w)
                {
                    dist[edge[j].v] = dist[edge[j].u] - edge[j].w;
                }
            }
        }

        bool flag = true;
        for(int j = 0; j < cnt; j++)
        {
            if(dist[edge[j].v] > dist[edge[j].u] - edge[j].w)
            {
                flag = false;
            }
        }

        printf("%s
", flag ? "Reliable" : "Unreliable");
    }
    return 0;
}