LeetCode--First Missing Positive

Given an unsorted integer array, find the first missing positive integer.

For example,
Given [1,2,0] return 3,
and [3,4,-1,1] return 2.

Your algorithm should run in O(n) time and uses constant space.

思路：桶排序(bucket sort)，每当nums[i]!=i+1的时候，将nums[i]与nums[nums[i]-1]交换，直到无法交换为止，终止条件是nums[i]==nums[nums[i]-1]。

class Solution {public:    int firstMissingPositive(vector<int>& nums) {        int n=nums.size();        bucket_sort(nums,n);        for(int i=0;i<n;i++){            if(nums[i]!=i+1) return i+1;        }        return n+1;    }    void bucket_sort(vector<int>&nums,int n){        for(int i=0;i<n;i++){            while(nums[i]!=i+1){                if(nums[i]<1||nums[i]>n||nums[i]==nums[nums[i]-1]) break;                swap(nums[i],nums[nums[i]-1]);            }        }    }};