minimum-moves-to-equal-array-elements-ii（好）

https://leetcode.com/problems/minimum-moves-to-equal-array-elements-ii/

package com.company;

import java.util.*;

// https://discuss.leetcode.com/topic/68736/java-just-like-meeting-point-problem
// 以上是整体解法,获得中位数中位数就可以获得结果 (just like meeting point problem)

// https://discuss.leetcode.com/topic/68758/java-o-n-time-using-quickselect/2
// 以上解法是 O(n) 获得中位数的方法 (其实是获得第K位结果的方法, Quick-select)

class Solution {
    // 对应上面的第一种方法
    public int minMoves2_old(int[] nums) {
        Arrays.sort(nums);
        int i = 0, j = nums.length - 1;
        int ret = 0;
        while (i < j) {
            ret += nums[j] - nums[i];
            i++;
            j--;
        }
        return ret;
    }

    // 对应上面的第二种方法
    public int minMoves2(int[] nums) {
        int mid = getPos(nums, nums.length/2+1, 0, nums.length-1);
        int ret = 0;
        for (int i=0; i<nums.length; i++) {
            ret += Math.abs(nums[i]-mid);
        }
        return ret;
    }

    private int getPos(int[] nums, int k, int start, int end) {
        int pivot = nums[end];
        int left = start;
        int right = end;

        while (left <= right) {
            while (left <= right && nums[left] < pivot) left++;
            while (left <= right && nums[right] >= pivot) right--;
            if (left > right) {
                break;
            }
            swap(nums, left, right);
        }
        swap(nums, left, end);
        if (k == left+1) {
            return nums[left];
        }
        if (k < left+1) {
            return getPos(nums, k, start, left-1);
        }
        else {
            return getPos(nums, k, left+1, end);
        }

    }

    private void swap(int[] nums, int a, int b) {
        int tmp = nums[a];
        nums[a] = nums[b];
        nums[b] = tmp;
    }

}

public class Main {

    public static void main(String[] args) throws InterruptedException {

        System.out.println("Hello!");
        Solution solution = new Solution();

        // Your Codec object will be instantiated and called as such:
        int[] nums = {1,2,3};
        int ret = solution.minMoves2(nums);
        System.out.printf("ret:%d\n", ret);

        System.out.println();

    }

}