Leetcode:First Missing Positive 第一个缺失的正数 桶排序

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.

class Solution {
public:
    int firstMissingPositive(int A[], int n) {
        assert(A != NULL && n >= 0);
        unordered_set<int> numSet;
        for (int i = 0; i < n; ++i) {
            numSet.insert(A[i]);
        }
        
        for (int i = 1; ; ++i) {
            auto iter = numSet.find(i);
            if (iter == numSet.end()) {
                return i;
            }
        }
    }
};

class Solution {
public:
    int firstMissingPositive(int A[], int n) {
        bucketSort(A, n);
        for (int i = 0; i < n; ++i) {
            if (A[i] != i + 1) {
                return i + 1;
            }
        }
        return n + 1;
        
    }
    
    void bucketSort(int A[], int n) {
        assert(A != NULL && n >= 0);
        for (int i = 0; i < n; ++i) {
            while (A[i] != i + 1) {
                if (A[i] <= 0 || A[i] > n || A[i] == A[A[i] - 1]) {
                    break;
                }
                std::swap(A[i], A[A[i] - 1]);
            }
        }
    }
};