【HDOJ】4109 Instrction Arrangement

最新推荐文章于 2018-05-13 10:32:00 发布

weixin_34293902

最新推荐文章于 2018-05-13 10:32:00 发布

阅读量72

点赞数

CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/bombe1013/p/4360170.html

本文介绍了一种使用SPFA算法解决差分约束问题的方法，通过C++代码实现，包括节点初始化、边添加及最短路径计算等功能。

差分约束。

 1 /* 4109 */
 2 #include <iostream>
 3 #include <queue>
 4 #include <vector>
 5 #include <algorithm>
 6 #include <cstdio>
 7 #include <cstring>
 8 #include <cstdlib>
 9 #include <climits>
10 using namespace std;
11 
12 #define MAXV 1005
13 #define MAXE 41005
14 #define INF  0x3f
15 
16 typedef struct {
17     int v, w, next;
18 } Edge_t;
19 
20 Edge_t E[MAXE];
21 int head[MAXV], L;
22 int dis[MAXV];
23 bool visit[MAXV];
24 int n, m;
25 
26 void init() {
27     for (int i=0; i<=n; ++i)
28         dis[i] = INT_MIN;
29     memset(head, -1, sizeof(int)*(n+1));
30     memset(visit, false, sizeof(bool)*(n+1));
31     L = 0;
32 }
33 
34 void addEdge(int u, int v, int w) {
35     E[L].v = v;
36     E[L].w = w;
37     E[L].next = head[u];
38     head[u] = L++;
39 }
40 
41 void spfa() {
42     int i, j, k;
43     int u, v, w;
44     queue<int> Q;
45 
46     visit[n] = true;
47     dis[n] = 0;
48     Q.push(n);
49 
50     while (!Q.empty()) {
51         u = Q.front();
52         Q.pop();
53         visit[u] = false;
54         for (i=head[u]; i!=-1; i=E[i].next) {
55             v = E[i].v;
56             w = E[i].w;
57             if (dis[v] < dis[u]+w) {
58                 dis[v] = dis[u] + w;
59                 if (!visit[v]) {
60                     visit[v] = true;
61                     Q.push(v);
62                 }
63             }
64         }
65     }
66 }
67 
68 int main() {
69     int i, j, k;
70 
71     #ifndef ONLINE_JUDGE
72         freopen("data.in", "r", stdin);
73         freopen("data.out", "w", stdout);
74     #endif
75 
76     while (scanf("%d %d",&n,&m) != EOF) {
77         init();
78         while (m--) {
79             scanf("%d%d%d", &i, &j, &k);
80             addEdge(j, i, k);
81         }
82         for (i=0; i<n; ++i)
83             addEdge(n, i, 0);
84         spfa();
85         k = INT_MIN;
86         for (i=0; i<=n; ++i)
87             k = max(k, dis[i]);
88         printf("%d\n", k+1);
89     }
90 
91     return 0;
92 }