统计子矩阵+二维前缀和+滑动窗口

题目链接：统计子矩阵
代码

#include<iostream>
using namespace std;

const int N = 505;

int num[N][N]; 

int main() {
	int n, m, k;
	cin >> n >> m >> k;
	int count = 0;
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= m; j++) {
			cin >> num[i][j];
			num[i][j] += num[i - 1][j] + num[i][j - 1] - num[i - 1][j - 1];
		}
	}
//打印二维前缀和效果 
//	for (int i = 1; i <= n; i++) {
//		for (int j = 1; j <= m; j++) {
//			cout << num[i][j] << " ";
//		}
//		cout << endl;
//	}
//for循环超时 
//	for (int x1 = 1; x1 <= n; x1++) {
//		for (int y1 = 1; y1 <= m; y1++) {
//			for (int x2 = x1; x2 <= n; x2++) {
//				for (int y2 = y1; y2 <= m; y2++) {
//					if (num[x2][y2] - num[x2][y1 - 1] - num[x1 - 1][y2] + num[x1 - 1][y1 - 1] <= k) {
//						count++;
////						cout << k << " " << z << " " << i << " " << j << "##" << endl;
//					}
////					cout << k << " " << z << " " << i << " " << j << endl;
//				}
//			}
//		}
////	}
//	cout << count;
	for (int l = 1; l <= m; l++) {
		for (int r = l; r <= m; r++) {
			for (int u = 1, d = 1; d <= n; d++) {
				while (u <= d && num[d][r] - num[d][l - 1] - num[u - 1][r] + num[u - 1][l - 1] > k) {
					u++;
				}
				count += d - u + 1;	
			}	
		}
	} 
	cout << count;
	return 0; 
}