P8783 [蓝桥杯 2022 省 B] 统计子矩阵

合集 - 洛谷(99)

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54.P8783 [蓝桥杯 2022 省 B] 统计子矩阵2024-02-15

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收起

原题链接

题解

1.当存在某个矩阵符合题意时，所有小于该矩阵的矩阵都符合题意
这是我们就可以想到用双指针

code

#include<bits/stdc++.h>
using namespace std;
int a[505][505]={0},sum[505][505]={0};
int n,m,k;
int check(int down,int right,int up,int left)
{
    return sum[down][right]-sum[up-1][right]-sum[down][left-1]+sum[up-1][left-1]<=k;
}
int main()
{
    cin>>n>>m>>k;
    for(int i=1;i<=n;i++)
        for(int j=1;j<=m;j++)cin>>a[i][j];

    for(int i=1;i<=n;i++)
        for(int j=1;j<=m;j++)sum[i][j]=sum[i][j-1]+sum[i-1][j]-sum[i-1][j-1]+a[i][j];

    int ans=0;
    for(int up=1;up<=n;up++)
    {
        for(int down=up;down<=n;down++)
        {
            int left=1;
            for(int right=1;right<=m;right++)
            {
                while(!check(down,right,up,left))left++;
                ans+=right-left+1;
            }
        }
    }

    cout<<ans<<endl;
    return 0;
}