OJ-Problems-Source/QUSTOJ/1769.cpp
2016-06-15 21:02:01 +08:00

87 lines
1.7 KiB
C++

#include <iostream>
using namespace std;
const int maxnum = 10005;
const int maxEdge= 50005;
const int maxint = 107391822;
// 边,
typedef struct Edge{
int u, v; // 起点,重点
int weight; // 边的权值
}Edge;
Edge edge[maxEdge]; // 保存边的值
int dist[maxnum]; // 结点到源点最小距离
int nodenum, edgenum, source; // 结点数,边数,源点
// 初始化图
void init()
{
// 输入结点数,边数,源点
cin >> nodenum >> edgenum ;
source=1;
for(int i=1; i<=nodenum; ++i)
dist[i] = maxint;
dist[source] = 0;
for(int i=1; i<=edgenum; i++)
{
cin >> edge[i].u >> edge[i].v >> edge[i].weight;
if(edge[i].u == source) //注意这里设置初始情况
dist[edge[i].v] = edge[i].weight;
/*
/// Another
edge[i+1].u=edge[i].v;
edge[i+1].v=edge[i].u;
edge[i+1].weight=-edge[i].weight;
if(edge[i+1].u == source) //注意这里设置初始情况
dist[edge[i+1].v] = edge[i+1].weight;
*/
}
}
// 松弛计算
void relax(int u, int v, int weight)
{
if(dist[v] > dist[u] + weight)
dist[v] = dist[u] + weight;
}
bool Bellman_Ford()
{
for(int i=1; i<=nodenum-1; ++i)
for(int j=1; j<=edgenum; ++j)
relax(edge[j].u, edge[j].v, edge[j].weight);
bool flag = 1;
// 判断是否有负环路
for(int i=1; i<=edgenum; ++i)
if(dist[edge[i].v] > dist[edge[i].u] + edge[i].weight)
{
flag = 0;
break;
}
return flag;
}
int main()
{
//freopen("input3.txt", "r", stdin);
init();
if(Bellman_Ford())
//for(int i = 1 ;i <= nodenum; i++)
cout << dist[nodenum] << endl;
else
throw "WTF??";
return 0;
}
/*
4 6
1 2 -5
2 3 -6
1 3 -9
2 4 -7
3 4 -8
1 4 6
*/