leetcode--First Missing Positive

[code]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) {

// Start typing your C/C++ solution below

// DO NOT write int main() function

if(n==0)return 1;

int i=0;

while(i<n)

{

    if(A[i]>0&&A[i]<=n)

    {

if(A[i]!=A[A[i]-1])

{

    int temp=A[i];

    A[i]=A[A[i]-1];

    A[temp-1]=temp;

    continue;

}

else i++;

}

    else 

    {

A[i]=0;i++;

}

}

i=0;

while(i<n)

{

    if(A[i]!=(i+1))return i+1;

    i++;

}

return n+1;

}

};