How Many Shortest Path

题目：

给出一张图，求解最短路有几条。处理特别BT。还有就是要特别处理map[i][i] = 0，数据有不等于0的情况！

竟然脑残到了些错floyd！

！。！！

！

14次wrong。！

！。。！

。。

算法：

先最短路处理，把在最短路上的边加入上。既是。dist[s][i] + map[i][j] == dist[s][j]表示从起点到i点加上当前边是最短路。把这个加入到网络流边集中。容量为1.然后，建立一个超级源点。容量为INF。

#include <iostream>
#include <algorithm>
#include <queue>
#include <vector>
#include <cstdio>
#include <cstring>
using namespace std;const int INF = 1 << 30;
const int MAXN = 200 + 10;
struct Edge{int from,to,cap,flow;Edge(){};Edge(int _from,int _to,int _cap,int _flow):from(_from),to(_to),cap(_cap),flow(_flow){};
};
vector<Edge> edges;
vector<int> G[MAXN];
int cur[MAXN],d[MAXN];
bool vst[MAXN];
int N,M,src,sink;int mat[MAXN][MAXN],dist[MAXN][MAXN];
int ss,tt;void init(){for(int i = 0;i <= N+5;++i)G[i].clear();edges.clear();
}void addEdge(int from,int to,int cap){edges.push_back(Edge(from,to,cap,0));edges.push_back(Edge(to,from,0,0));int sz = edges.size();G[from].push_back(sz - 2);G[to].push_back(sz - 1);
}void flody(){memcpy(dist,mat,sizeof(mat));for(int i = 0;i < N;++i)for(int j = 0;j < N;++j)dist[i][j] = (dist[i][j]==-1?

INF:dist[i][j]); for(int k = 0;k < N;++k) for(int i = 0;i < N;++i) for(int j = 0;j < N;++j){ // if(dist[i][k] == INF||dist[k][j] == INF) continue; if(dist[i][k] < INF && dist[k][j] < INF&&dist[i][j] > dist[i][k] + dist[k][j]) dist[i][j] = dist[i][k] + dist[k][j]; } } bool BFS(){ memset(vst,0,sizeof(vst)); queue<int> Q; Q.push(src); d[src] = 0; vst[src] = 1; while(!Q.empty()){ int u = Q.front(); Q.pop(); for(int i = 0;i < (int)G[u].size();++i){ Edge& e = edges[G[u][i]]; if(!vst[e.to] && e.cap > e.flow){ vst[e.to] = 1; d[e.to] = d[u] + 1; Q.push(e.to); } } } return vst[sink]; } int DFS(int x,int a){ if(x == sink || a == 0) return a; int flow = 0,f; for(int& i = cur[x];i < (int)G[x].size();++i){ Edge& e = edges[G[x][i]]; if(d[e.to] == d[x] + 1 && (f = DFS(e.to,min(a,e.cap - e.flow))) > 0){ e.flow += f; edges[G[x][i]^1].flow -= f; flow += f; a -= f; if(a == 0) break; } } return flow; } int maxFlow(){ int flow = 0; while(BFS()){ memset(cur,0,sizeof(cur)); flow += DFS(src,INF); } return flow; } int main() { // freopen("Input.txt","r",stdin); while(~scanf("%d",&N)){ init(); for(int i = 0;i < N;++i) for(int j = 0;j < N;++j){ scanf("%d",&mat[i][j]); } for(int i = 0;i < N;++i) mat[i][i] = 0; scanf("%d%d",&ss,&tt); flody(); if(ss == tt){ printf("inf\n"); continue; } src = N + 2; sink = tt; addEdge(src,ss,INF); // 建图 for(int i = 0;i < N;++i){ if(dist[ss][i] == INF) continue; for(int j = 0;j < N;++j){ if(i == j) continue; if(dist[ss][j] == INF||mat[i][j] == -1) continue; if(dist[ss][i] + mat[i][j] == dist[ss][j]){ //该边是否在最短路上 addEdge(i,j,1); } } } printf("%d\n",maxFlow()); } return 0; }