LeetCode ---- First Missing Positive

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

For example,
Given[1, 2, 0]Return3,
And[3, 4,-1, 1]Return2.

Your algorithm shold run inO(N) Time and uses constant space.

Analysis:

Thought 1: first sort and then scan the array again .. O (nlgn)

Idea 2: A total of n numbers. For those numbers greater than n, it will not be our first missing positive integer.

It is equivalent that we have n buckets. Each bucket should start from 1 to n, and the first unsatisfied bucket is our result.

Class Solution {public: int firstMissingPositive (int A [], int n) {bucket_sort (A, n); for (int I = 0; I

 
  
N | A [I] = A [A [I]-1]) break; swap (A [I], A [A [I]-1]) ;}}};