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) {
for (int i=0; i<n;) {
if (A[i] != i+1 && A[i] > 0 && A[i] <= n && A[i] != A[A[i]-1])
swap(A[i], A[A[i]-1]);
else
......
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