CCF邻域均值

试题背景

问题描述

输入格式

输出格式

样例

输入

4 16 1 6
0 1 2 3
4 5 6 7
8 9 10 11
12 13 14 15

输出

7

C++求解

暴力方法

#include<iostream>
using namespace std;
int main()
{
    int n,L,r,t;
    int result=0;
    cin>>n>>L>>r>>t;
    int A[n][n];
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            cin>>A[i][j];
        }
    }
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            //i j
            int sum=0;
            int num=0;
            for(int k=i-r;k<=i+r;k++){
                if(k>=0&&k<n){
                    for(int p=j-r;p<=j+r;p++){
                        if(p>=0&&p<n){
                            sum+=A[k][p];
                            num++;
                        }
                    }
                }

            }
            double avg=(double)sum/num;
            if(avg<=t) result++;
        }
    }
    cout<<result;
    return 0;
}

一些聪明的方法
先求出每一列第一个对应数的sum和num，在此基础上进行加减求这一行的数的sum和num

#include <iostream>
using namespace std;
int main()
{
    int n, L, r, t;
    int matrix[600][600];
    int res = 0;
    int temp;
    cin >> n >> L >> r >> t;
 
    //input
    for(int i = 0; i < n; i++)
    {
        for(int j = 0; j < n; j++)
        {
            cin >> temp;
            matrix[i][j] = temp;
        }
    }
 
 
    //data process
    int sum = 0, num = 0, lastsum = 0, lastnum = 0;
    for(int i = 0; i < n; i++)//先求第一列
    {
        sum = num = 0;
        int bound_x = i + r > n - 1? n - 1 : i + r;
        int bound_y = 0 + r > n - 1? n - 1 : 0 + r;
        int start_x = i - r > 0 ? i - r : 0;
        for(int k = start_x; k <= bound_x; k++)
            for(int m = 0; m <= bound_y; m++)//第一排的y都从0开始
            {
                num++;
                sum += matrix[k][m];
            }
        double avg = (double)sum / num;
        lastnum = num; lastsum = sum;
        if(avg <= t)
            res++;
 
 
 
        for(int j = 1; j < n; j++)//每一列对应的排
        {
            sum = lastsum;
            if(j - r <= 0)
            {
                num = lastnum + bound_x - start_x + 1;
                for(int m = start_x; m <= bound_x; m++)
                    sum += matrix[m][j+r];
                avg = (double)sum / num;
            }
            else if(j + r > n - 1)
            {
                num = lastnum - (bound_x - start_x + 1);
                for(int m = start_x; m <= bound_x; m++)
                    sum -= matrix[m][j - r - 1];
                avg = (double)sum / num;
            }
            else
            {
                num = lastnum;
                for(int m = start_x; m <= bound_x; m++)
                    sum += matrix[m][j+r] - matrix[m][j - r - 1];
                avg = (double)sum / num;
            }
            if(avg <= t)
                res++;
            lastnum = num; lastsum = sum;//替换一下
        }
    }
    cout << res;
    return 0;
}