《程序员代码面试指南》第八章 数组和矩阵问题 计算数组的小和

题目

计算数组的小和

java代码

package com.lizhouwei.chapter8;

/**
 * @Description: 计算数组的小和
 * @Author: lizhouwei
 * @CreateDate: 2018/5/8 20:29
 * @Modify by:
 * @ModifyDate:
 */
public class Chapter8_13 {

    public int smallSum(int[] arr) {
        int[] res = new int[arr.length];
        return mergeSort(arr, 0, arr.length - 1, res);
    }

    public int mergeSort(int[] arr, int left, int right, int[] res) {
        if (left >= right) {
            return 0;
        }
        int mid = (left + right) / 2;
        int len1 = mergeSort(arr, left, mid, res);
        int len2 = mergeSort(arr, mid + 1, right, res);
        int len3 = 0;
        int leftIndex = left;
        int rightIndex = mid + 1;
        int k = left;
        while (leftIndex <= mid && rightIndex <= right) {
            if (arr[leftIndex] < arr[rightIndex]) {
                len3 = len3 + arr[leftIndex] * (right - rightIndex + 1);
                res[k++] = arr[leftIndex++];
            } else {
                res[k++] = arr[rightIndex++];
            }
        }
        while (leftIndex <= mid) {
            res[k++] = arr[leftIndex++];
        }
        while (rightIndex <= right) {
            res[k++] = arr[rightIndex++];
        }
        leftIndex = left;
        while (leftIndex < right) {
            arr[leftIndex] = res[leftIndex++];
        }
        return len1 + len2 + len3;
    }

    //测试
    public static void main(String[] args) {
        Chapter8_13 chapter = new Chapter8_13();
        int[] arr = {1, 3, 5, 2, 4, 6};
        System.out.print("数组 arr = {1, 3, 5, 2, 4, 6}中最小和为:");
        int maxLen = chapter.smallSum(arr);
        System.out.print(maxLen);
    }
}

结果