引用链接http://www.cnblogs.com/north_dragon/archive/2010/05/30/1747697.html
http://www.cnblogs.com/AbandonZHANG/archive/2012/07/26/2610833.html
1 #include <iostream> 2 #include <string> 3 #include <vector> 4 #include <cstdlib> 5 #include <cmath> 6 #include <map> 7 #include <algorithm> 8 #include <list> 9 #include <ctime> 10 #include <set> 11 #include <string.h> 12 #include <queue> 13 using namespace std; 14 15 int maxData = 0x3fffffff; 16 17 bool relax(int u, int v, int w) { 18 if (v > u + w) { 19 v = u + w; 20 return true; 21 } else 22 return false; 23 } 24 25 bool bellman_ford(int s, vector<int> &d, vector<vector<int> > path) { 26 int n = d.size(); 27 int i, j, k; 28 bool judge; 29 for (i = 0; i < n; ++i) { 30 d[i] = maxData; //将除源点以外的其余点的距离设置为无穷大 31 } 32 d[s] = 0; 33 for (i = 0; i < n - 1; i++) { 34 for (j = 0; j < n; j++) { 35 for (k = 0; k < n; k++) { 36 judge = relax(d[j], d[k], path[j][k]); 37 if (judge) { 38 d[k] = d[j] + path[j][k]; 39 } 40 41 } 42 } 43 } 44 45 for (j = 0; j < n; j++) { 46 for (k = 0; k < n; k++) { 47 judge = relax(d[j], d[k], path[j][k]); 48 if (judge) { 49 return true; 50 } 51 52 } 53 } 54 55 return false; 56 } 57 58 bool SPFA(int s, vector<int> &d, vector<vector<int> > path) { 59 int n = d.size(); 60 queue<int> myqueue; 61 int i; 62 63 for (i = 0; i < n; ++i) { 64 d[i] = maxData; //将除源点以外的其余点的距离设置为无穷大 65 } 66 vector<bool> final(n, false); //记录顶点是否在队列中，SPFA算法可以入队列多次 67 vector<int> cnt(n, 0); //记录顶点入队列次数 68 d[s] = 0; //源点的距离为0 69 final[s] = true; 70 cnt[s]++; //源点的入队列次数增加 71 myqueue.push(s); 72 int topint; 73 while (!myqueue.empty()) { 74 topint = myqueue.front(); 75 myqueue.pop(); 76 final[topint] = false; 77 for (i = 0; i < n; ++i) { 78 if (d[topint] < maxData && d[i] > d[topint] + path[topint][i]) { 79 d[i] = d[topint] + path[topint][i]; 80 if (!final[i]) { //判断是否在当前的队列中 81 final[i] = true; 82 cnt[i]++; 83 if (cnt[i] >= n) //当一个点入队的次数>=n时就证明出现了负环。 84 return true; 85 myqueue.push(i); 86 } 87 } 88 } 89 } 90 return false; 91 } 92 93 int main() { 94 vector<vector<int> > path(4, vector<int>(4, maxData)); 95 vector<int> d(4, maxData); 96 bool judge; 97 for (int i = 0; i < 4; i++) 98 path[i][i] = 0; 99 path[0][1] = path[1][0] = path[2][3] = 1; 100 path[1][2] = 5; 101 path[0][2] = 3; 102 103 judge = SPFA(0, d, path); 104 if (!judge) 105 for (int i = 0; i < 4; i++) 106 cout << d[i] << endl; 107 else 108 cout << "存在负权回路\n"; 109 110 judge = bellman_ford(0, d, path); 111 if (!judge) 112 for (int i = 0; i < 4; i++) 113 cout << d[i] << endl; 114 else 115 cout << "存在负权回路\n"; 116 117 path[1][2] = 1; 118 path[2][0] = -3; 119 judge = SPFA(0, d, path); 120 if (!judge) 121 for (int i = 0; i < 4; i++) 122 cout << d[i] << endl; 123 else 124 cout << "存在负权回路\n"; 125 126 judge = bellman_ford(0, d, path); 127 if (!judge) 128 for (int i = 0; i < 4; i++) 129 cout << d[i] << endl; 130 else 131 cout << "存在负权回路\n"; 132 133 return 0; 134 135 }