leetcode - First Missing Positive

题目描述：点击此处

利用到原来的数组空间，不知道符不符合题意。

class Solution {
public:
  int firstMissingPositive(int A[], int n) {
    // Start typing your C/C++ solution below
    // DO NOT write int main() function
    int i, j;
    for (i=0; i<n; i++){
      if (A[i]<=0 || A[i]>n)
        A[i] = 0;
    }
    i=0;
    while (i<n){
      if (A[i]>0){
        j = A[i] - 1;
        if (A[j]>0 && A[A[j]-1]!=-1){
          A[i] = A[j];
          A[j] =-1;
          continue;
        }
        A[j] = -1;
        A[i] = 0;
      }
      i++;
    }
    i=0;
    while (i<n && A[i]==-1)
      i++;
    return i+1;
  }
};