《程序员代码面试指南》第八章 数组和矩阵问题 未排序数组中累加和小于或等于给定值的最长子数组长度

题目

未排序数组中累加和小于或等于给定值的最长子数组长度

java代码

package com.lizhouwei.chapter8;

/**
 * @Description: 未排序数组中累加和小于或等于给定值的最长子数组长度
 * @Author: lizhouwei
 * @CreateDate: 2018/5/8 20:14
 * @Modify by:
 * @ModifyDate:
 */
public class Chapter8_12 {

    public int maxLength(int[] arr, int k) {
        int sum = 0;
        int[] helpArr = new int[arr.length + 1];
        for (int i = 0; i < arr.length; i++) {
            sum = sum + arr[i];
            helpArr[i + 1] = Math.max(sum, helpArr[i]);
        }
        sum = 0;
        int len = 0;
        int maxLen = 0;
        int index = 0;
        for (int i = 0; i < arr.length; i++) {
            sum = sum + arr[i];
            index = bs(helpArr, sum - k);
            len = index == -1 ? 0 : i - index + 1;
            maxLen = Math.max(maxLen, len);
        }
        return maxLen;
    }

    public int bs(int[] helpArr, int num) {
        int left = 0;
        int right = helpArr.length - 1;
        int mid = 0;
        int res = -1;
        while (left < right) {
            mid = (left + right) / 2;
            if (helpArr[mid] < num) {
                left = mid + 1;
            } else {
                res = mid;
                right = mid - 1;
            }
        }
        return res;
    }

    //测试
    public static void main(String[] args) {
        Chapter8_12 chapter = new Chapter8_12();
        int[] arr = {3, -2, -4, 0, 6};
        System.out.print("数组 arr = {3, -2, -4, 0, 6}中和小于-2的最长子数组长度为:");
        int maxLen = chapter.maxLength(arr, -2);
        System.out.print(maxLen);
    }
}

结果