sgu 218 分类： sgu 2015-06-21 17:04 22人阅读 评论(0) 收藏

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二分答案+二分图匹配
时间复杂度：O(n2∗log2n)

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#include<cstdio>
#include<cstdlib>
#include<ctime>
#include<cmath>
#include<cstring>
#include<map>
#include<string>
#include<stack>
#include<queue>
#include<utility>
#include<iostream>
#include<algorithm>

const int maxn = 505, INF = 0x3f3f3f3f;

int n, w[maxn][maxn];
bool hash[maxn];
int ans, link[maxn];

bool find(int x, int k)
{
    for(int y = 1; y <= n; y++)
        if(!hash[y] && w[x][y] <= k)
        {
            hash[y] = true;
            if(!link[y] || find(link[y],k))
            {
                link[y] = x;
                return true;
            }
        }

    return false;   
}

bool check(int key)
{
    memset(link, 0, sizeof(link));
    for(int i = 1; i <= n; i++)
    {
        memset(hash, false, sizeof(hash));
        if(!find(i, key)) return false;
    }
    return true;
}

void MainWork(int l,int r)
{
    while(l + 1 != r)
    {
        int mid = (l + r)>>1;

        if(check(mid))
            r = mid;
        else
            l = mid;
    }

    ans = r;
}

int main()
{
    int wmax = -INF, wmin = INF;

#ifndef ONLINE_JUDGE
    freopen("sgu218.in","r",stdin);
    freopen("sgu218.out","w",stdout);
#endif

    std::cin >> n;

    for(int i = 1; i <= n; i++)
        for(int j = 1; j <= n; j++)
        {
            std::cin >> w[i][j];
            wmax = std::max(wmax, w[i][j]);
            wmin = std::min(wmin, w[i][j]);
        }

    MainWork(wmin - 1, wmax + 1);

    std::cout << ans << std::endl, check(ans);
    for(int i = 1; i <= n; i++)
        std::cout << link[i] << ' ' << i << std::endl;


#ifndef ONLINE_JUDGE
    fclose(stdin);
    fclose(stdout);
#endif
    return 0;
}

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