leetcode 41. First Missing Positive

传送门

41. First Missing Positive

 

QuestionEditorial Solution

 My Submissions

 

• Total Accepted: 69874
• Total Submissions: 288517
• Difficulty: Hard

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.

Subscribe to see which companies asked this question

Hide Tags

 Array

Hide Similar Problems

 (M) Missing Number (H) Find the Duplicate Number

 

 

题解转自：

http://blog.csdn.net/sbitswc/article/details/31870975

 

桶排序，每次当A[i]!= i的时候，将A[i]与A[A[i]]交换，直到无法交换位置。终止条件是 A[i]== A[A[i]]。
然后i -> 0 到n走一遍就好了。

 

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