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！
居然脑残到了些错floyd！！！！！！14次wrong！！！！！！！！
算法：
先最短路处理，把在最短路上的边添加上。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
#include
#include
#include
#include
#include
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
edges; vector
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
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; }