这道题为有向图有相交边的情况。。不能直接求最大匹配
先用floyd处理一下边
//
// main.cpp
// wzazzy
//
// Created by apple on 2018/10/23.
// Copyright © 2018年 apple. All rights reserved.
//
#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<string.h>
#include<queue>
#include<stack>
#include<list>
#include<map>
#include<set>
#include<vector>
using namespace std;
typedef long long int ll;
const int maxn =1500+10;
const int maxm=10000;
const int mod =1e9+7;
const int INF=0x3f3f3f3f;
//**********************************
int n, m, maze[510][510], linker[510];
bool used[510];
void Floyd(){
for(int k = 1; k <= n; ++k)
for(int i = 1; i <= n; ++i)
if(maze[i][k]){
for(int j = 1; j <= n; ++j)
if(maze[k][j]) maze[i][j] = 1;
}
}
bool dfs(int u){
for(int v = 1; v <= n; ++v){
if(maze[u][v] && !used[v]){
used[v] = true;
if(linker[v] == -1 || dfs(linker[v])){
linker[v] = u;
return true;
}
}
}
return false;
}
int hungary(){
int res = 0;
memset(linker, -1, sizeof(linker));
for(int i = 1; i <= n; ++i){
memset(used, false, sizeof(used));
if(dfs(i)) ++res;
}
return res;
}
int main()
{
while(~scanf("%d%d", &n, &m) && (n||m)){
memset(maze, 0, sizeof(maze));
int u, v;
for(int i = 0; i < m; ++i){
scanf("%d%d", &u, &v);
maze[u][v] = 1;
}
Floyd();
int ans = hungary();
printf("%d\n", n-ans);
}
}
还可以更快,使用bitset优化。代码如下
//
// main.cpp
// wzazzy
//
// Created by apple on 2018/10/23.
// Copyright © 2018年 apple. All rights reserved.
//
#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<string.h>
#include<queue>
#include<stack>
#include<list>
#include<map>
#include<set>
#include<bitset>
#include<vector>
using namespace std;
typedef long long int ll;
const int maxn =1500+10;
const int maxm=10000;
const int mod =1e9+7;
const int INF=0x3f3f3f3f;
//**********************************
int n, m, linker[510];
bitset<510> maze[510];
bool used[510];
void floyd()
{
for(int i=1;i<=n;i++)
for(int j=1;j<=n;j++)
if(maze[j][i]) maze[j]|=maze[i];
}
bool dfs(int u){
for(int v = 1; v <= n; ++v){
if(maze[u][v] && !used[v]){
used[v] = true;
if(linker[v] == -1 || dfs(linker[v])){
linker[v] = u;
return true;
}
}
}
return false;
}
int hungary(){
int res = 0;
memset(linker, -1, sizeof(linker));
for(int i = 1; i <= n; ++i){
memset(used, false, sizeof(used));
if(dfs(i)) ++res;
}
return res;
}
int main()
{
while(~scanf("%d%d", &n, &m) && (n||m)){
memset(maze, 0, sizeof(maze));
int u, v;
for(int i = 0; i < m; ++i){
scanf("%d%d", &u, &v);
maze[u][v] = 1;
}
floyd();
int ans = hungary();
printf("%d\n", n-ans);
}
}