[LeetCode][JavaScript]Permutations

Permutations

Given a collection of numbers, return all possible permutations.

For example,
[1,2,3] have the following permutations:
[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1].

https://leetcode.com/problems/permutations/

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数字排列。

循环每一位数字，每个数都和所有数交换（包括自己）。

/**
 * @param {number[]} nums
 * @return {number[][]}
 */
var permute = function(nums) {
    var result = [];
    getPermute(0);
    return result;

    function getPermute(index){
        if(index === nums.length){
            result.push(nums.slice(0));
            return;
        }
        for(var i = index; i < nums.length; i++){
            switchNum(i, index);
            getPermute(index + 1);
            switchNum(i, index);
        }
    }
    function switchNum(i, j){
        if(i === j) return;
        var tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }
};