DFS与最大匹配

其实就是个DFS。

题目：http://acm.swust.edu.cn/oj/problem/0827/

 

#include "iostream"
#include "string"
#include "cstring"
#include "algorithm"
using namespace std;

#define maxn 105
#define INF 0xFFFFFFF
int map[maxn][maxn],  mid, k, N, M;
int Link[maxn]; //记录行的状态
int used[maxn]; //记录列的状态

bool dfs(int u)//行
{
    for(int v=1; v<=M; v++) //列++
    {
        if(map[u][v]>=k && map[u][v]<=k+mid && !used[v])
        {
            used[v] = 1;
            if(Link[v]==-1 || dfs(Link[v]))
            {
                Link[v] = u;
                return true;
            }
        }
    }
    return false;
}

bool OK()
{
    memset(Link, -1, sizeof(Link));
    for(int i=1; i<=N; i++) //行++
    {
        memset(used, 0, sizeof(used));
        if(!dfs(i)) return false;
    }
    return true;
}

int main()
{
    while(cin>>N>>M)
    {
        int Max = 0;
        int Min = INF;
        for(int i=1; i<=N; i++)
            for(int j=1; j<=M; j++)
            {
                cin>>map[i][j];
                if(map[i][j]>Max) Max = map[i][j];
                if(map[i][j]<Min) Min = map[i][j];
            }
        int left=0, right=Max-Min, ans;
        while(left <= right)
        {
            mid = (left+right)/2;
            int flag = 0;
            for(k=Min; k+mid<=Max; k++)
            {
                if(OK())
                {
                    ans = mid;
                    flag = 1;
                    break;
                }
            }
            if(flag) right = mid-1;
            else left = mid+1;
        }
        cout<<ans<<endl;
    }
}