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  • Lintcode: Median

    Given a unsorted array with integers, find the median of it. 
    
    A median is the middle number of the array after it is sorted. 
    
    If there are even numbers in the array, return the N/2-th number after sorted.
    
    Example
    Given [4, 5, 1, 2, 3], return 3
    
    Given [7, 9, 4, 5], return 5
    
    Challenge
    O(n) time.

    Quicksort的变形,quickselect,跟Kth largest Element很像

     1 public class Solution {
     2     /**
     3      * @param nums: A list of integers.
     4      * @return: An integer denotes the middle number of the array.
     5      */
     6     public int median(int[] nums) {
     7         // write your code here
     8         int len  = nums.length;
     9         if (len%2 == 0) return search(nums, len/2, 0, len-1);
    10         else return search(nums, len/2+1, 0, len-1);
    11     }
    12     
    13     public int search(int[] nums, int k, int start, int end) {
    14         int l=start, r=end;
    15         int pivot = r;
    16         while (true) {
    17             while (nums[l] < nums[pivot] && l<r) {
    18                 l++;
    19             }
    20             while (nums[r] >= nums[pivot] && l<r) {
    21                 r--;
    22             }
    23             if (l == r) break;
    24             swap(nums, l, r);
    25         }
    26         swap(nums, l, end);
    27         if (k == l+1) return nums[l];
    28         else if (k > l+1) return search(nums, k, l+1, end);
    29         else return search(nums, k, start, l-1);
    30     }
    31     
    32     public void swap(int[] nums, int l, int r) {
    33         int temp = nums[l];
    34         nums[l] = nums[r];
    35         nums[r] = temp;
    36     }
    37 }
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  • 原文地址:https://www.cnblogs.com/EdwardLiu/p/4340933.html
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