Bellman-Ford算法：POJ No.3169 Layout 差分约束

 #define _CRT_SECURE_NO_WARNINGS
 /*
 4 2 1
 1 3 10 2 4 20
 2 3 3
 */
 #include <iostream>
 #include <algorithm>
 #include <cstdio>
 #include <cstdlib>
 using namespace std;

 const int maxn =  + ;
 const int INF = ;
 //输入
 int N, ML, MD;
 int AL[maxn], BL[maxn], DL[maxn];
 int AD[maxn], BD[maxn], DD[maxn];

 int d[maxn];

 void solve()
 {
     fill(d, d + N, INF);
     d[] = ;

     //用Bellman-Ford算法计算d
     for (int k = ; k < N; k++) {
         //从i+1到i的权值为0
         for (int i = ; i +  < N; i++) {
             if (d[i + ] < INF) d[i] = min(d[i], d[i + ]);
         }
         //从AL到BL的权值为DL
         for (int i = ; i < ML; i++) {
             if (d[AL[i] - ] < INF) {
                 d[BL[i] - ] = min(d[BL[i] - ], d[AL[i] - ] + DL[i]);
             }
         }
         //从BD到AD的权值为-DD
         for (int i = ; i < MD; i++) {
             if (d[BD[i] - ] < INF) {
                 d[AD[i] - ] = min(d[AD[i] - ], d[BD[i] - ] - DD[i]);
             }
         }
     }
     int res = d[N - ];
     if (d[] < ) {
         //存在负边无解
         res = -;
     }
     else if (res == INF) {
         res = -;
     }
     printf("%d\n", res);
 }

 void input()
 {
     cin >> N >> ML >> MD;
     for (int i = ; i < ML; i++) {
         cin >> AL[i] >> BL[i] >> DL[i];
     }
     for (int i = ; i < MD; i++) {
         cin >> AD[i] >> BD[i] >> DD[i];
     }
 }

 int main()
 {
     input();
     solve();
     return ;
 }