【LeetCode】442. Find All Duplicates in an Array

Given an array of integers, 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.

Find all the elements that appear twice in this array.

Could you do it without extra space and in O(n) runtime?

Example:

Input:
[4,3,2,7,8,2,3,1]

Output:
[2,3]

很简单的一个题目，要求了事件复杂度是o（n）。

用hash表来做。

/**
 * @param {number[]} nums
 * @return {number[]}
 */
var findDuplicates = function(nums) {
    var arr=[];
    var ret=[];
    for(var i=nums.length-1;i>=0;i--){
        if(arr[nums[i]]){
            ret.push(nums[i]);
        }else{
            arr[nums[i]]=true;
        }
    }
    return ret;
};