wenbao与差分约束

Posted 2020-10-31 wenbao

 

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

 

 

 1 #include "iostream"
 2 #include <string.h>
 3 #include <stdio.h>
 4 using namespace std;
 5 
 6 #define INF 1e9
 7 const int maxn = 10009*2;
 8 int n, ml, md, index, m;
 9 int head[maxn], to[maxn], pre[maxn], w[maxn], queue[maxn], dis[maxn], cnt[maxn];
10 
11 void init() {
12     index = 1;
13     for(int i = 1; i <= n; ++i) head[i] = 0, cnt[i] = 0;
14 }
15 
16 void add(int x, int y, int z) {
17     to[index] = y;
18     w[index] = z;
19     pre[index] = head[x];
20     head[x] = index++;
21 }
22 
23 bool mark[maxn];
24 
25 int spfa() {
26     int front = 0, rear = 0;
27     for(int i = 1; i <= n; ++i) {
28         dis[i] = INF;
29         add(i, i-1, 0);
30     }
31     dis[1] = 0;
32     queue[rear++] = 1;
33     while(front != rear) {
34         int k = queue[front++];
35         mark[k] = false;
36         for(int i = head[k]; i; i = pre[i]){
37             if(dis[k] + w[i] < dis[to[i]]) {
38                 dis[to[i]] = dis[k] + w[i];
39                 if(!mark[to[i]]) {
40                     if(++cnt[to[i]] > n) return -1;
41                     queue[rear++] = to[i];
42                     mark[to[i]] = true;
43                 }
44             }
45         }
46     }
47     if(dis[n] == INF) return -2;
48     return dis[n];
49 }
50 
51 int main() {
52 #ifdef wenbao
53     freopen("in", "r", stdin);
54 #endif
55     while(~scanf("%d%d%d", &n, &ml, &md)) {
56         init();
57         int x, y, z;
58         for(int i = 0; i < ml; ++i) {
59             scanf("%d%d%d", &x, &y, &z);
60             add(x, y, z);
61         }
62         for(int i = 0; i < md; ++i) {
63             scanf("%d%d%d", &x, &y, &z);
64             add(y, x, -z);
65         }
66         printf("%d\n", spfa());
67     }
68     return 0;
69 }

 

 

 

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