D. Monitor Educational Codeforces Round 28

http://codeforces.com/contest/846/problem/D

二分答案

适合于：

判断在t时候第一次成立

哪个状态是最小代价

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <time.h>
#include <string>
#include <set>
#include <map>
#include <list>
#include <stack>
#include <queue>
#include <vector>
#include <bitset>
#include <ext/rope>
#include <algorithm>
#include <iostream>
using namespace std;
#define ll long long
#define minv 1e-6
#define inf 1e9
#define pi 3.1415926536
#define E  2.7182818284
const ll mod=1e9+7;//998244353
const int maxn=5e2+10;

struct node
{
    int x,y,t;
}f[maxn*maxn];

int K,s,t,a[maxn][maxn],tot[maxn][maxn]={0};

int cmp(node a,node b)
{
    return a.t<b.t;
}

bool judge()
{
    int i,j;
    for (i=K;i<=s;i++)
        for (j=K;j<=t;j++)
            if (tot[i][j]-tot[i-K][j]-tot[i][j-K]+tot[i-K][j-K]==K*K)
                return 1;
    return 0;
}

int main()
{
    int q,i,j,l,r,m;
    scanf("%d%d%d%d",&s,&t,&K,&q);
    for (i=1;i<=q;i++)
        scanf("%d%d%d",&f[i].x,&f[i].y,&f[i].t);

    sort(f+1,f+q+1,cmp);

    l=1,r=q;
    while (l<=r)
    {
        memset(a,0,sizeof(a));
        m=(l+r)>>1;

        for (i=1;i<=m;i++)
            a[f[i].x][f[i].y]=1;
        for (i=1;i<=s;i++)
            for (j=1;j<=t;j++)
                tot[i][j]=tot[i-1][j]+tot[i][j-1]-tot[i-1][j-1]+a[i][j];
        if (judge())
            r=m-1;
        else
            l=m+1;
    }
    if (l==q+1)
        printf("-1");
    else
        printf("%d",f[l].t);
    return 0;
}
/*
2 2 2 4
1 2 1
1 1 4
2 2 3
2 1 2

2 2 1 4
1 2 1
1 1 4
2 2 3
2 1 2

2 2 2 0
*/