累加和小于或等于定值得最长子数组的长度

Posted 2020-09-15 起个po名真费劲

package com.hzins.suanfa;
/**
 * 累加和小于或等于定值得最长子数组的长度
 * @author Administrator
 *
 */
public class Demo1 {
    public static int maxLength(int[] arr, int k){
        int[] h = new int[arr.length + 1];
        int sum = 0;
        h[0] = sum;
        for(int i = 0;i !=arr.length;i ++){
            sum +=arr[i];
            h[i + 1] = h[i] + Math.max(sum, h[i]);
        }
        sum = 0;
        int res=  0;
        int pre= 0;
        int len = 0;
        for(int i = 0;i != arr.length;i++){
            sum +=arr[i];
            pre = getLessIndex(h, sum - k);
            len = pre == -1 ? 0 : i - pre + 1;
            res = Math.max(res, len);
        }
        return res;
    }

    /**
     * 在【】h中第一个大于等于i的数的位置
     * @param h
     * @param i
     * @return
     */
    private static int getLessIndex(int[] h, int i) {
        int left = 0;
        int right = h.length - 1;
        int mid = 0;
        int res = -1;
        while(left <= right){
            mid = (left + right) / 2;
            if(h[mid] >= i){
                right = mid - 1;
                res = mid;
            }else{
                left = mid + 1;
            }
        }
        return res;
    }
    public static void main(String[] args) {
        int[] array = {1,-2,3,-4,5,6,-6,7,-7,8};
        System.out.println(maxLength(array, -1));
        
    }
}