AcWing 4395. 最大子矩阵——Java(二分+前缀和+最小区间和)

import java.util.Arrays;
import java.util.Scanner;

public class Main {
	static long[] lena = new long[100000];
	static long[] lenb = new long[100000];
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] a = new int[n];
		int[] b = new int[m];
		long[] aq = new long[n+1];
		long[] bq = new long[m+1];
		for (int i = 1; i <= a.length; i++) {
			a[i-1] = sc.nextInt();
			aq[i] = aq[i-1] + a[i-1];
		}
		for (int i = 1; i <= b.length; i++) {
			b[i-1] = sc.nextInt();
			bq[i] = bq[i-1] + b[i-1];
		}
		int x = sc.nextInt();
		Arrays.fill(lena, Integer.MAX_VALUE);
		Arrays.fill(lenb, Integer.MAX_VALUE);

		//记录a b数组长度为len时的最小区间和
	    for (int len = 1; len <= n; len ++ )
	    {
	        for (int l = 1; l <= n - len + 1; l ++ )
	        {
	            int r = l + len - 1;
	            lena[len] = Math.min(lena[len], aq[r] - aq[l - 1]);
	        }
	    }
		for (int len = 1; len <= m; len ++) {
			for (int l = 1; l <= m - len + 1; l++) {
				int r = l + len -1;
				lenb[len] = Math.min(lenb[len], bq[r] - bq[l - 1]);
			}
		}
		long ans = 0;
		for (int i = 1; i <= n; i++) {
			int l = 1,r = m;
			while(l < r) {
				int mid = (l+r+1)/2;
				if (check(i,mid,x)) {
					l = mid;
				}else {
					r = mid - 1;
				}
			}
			 if(lena[i] * lenb[l] <= x) {
				  ans = Math.max(ans, l*i);
			 }
		}
		System.out.println(ans);
	}
	public static boolean check(int i ,int mid,int x) {
			return lena[i]*lenb[mid] <= x;
	}
}