Given an unsorted integer array,find the first missing positive integer.
For example,
Given [1,2,0] return 3,
and [3,4,⑴,1] return 2.
Your algorithm should run in O(n) time and uses constant space.
题意：找到第1个最小的正整数。思路：由于要求不能用到额外的空间，题目有暗示：答案在[1,n+1]之间。每一个位置都试着将这个位置的值换到对应的下标，这样第1个位置出现不是相应的值的时候就是答案，还有就是要是都能对应，那末n+1就是解
class Solution {
public:
int firstMissingPositive(int A[],int n) {
for (int i = 0; i < n; i++) A[i]--;
for (int i = 0; i < n; i++) {
while (A[i] != i && A[i] >= 0 && A[i] < n) {
if (A[i] == A[A[i]]) break;
swap(A[i],A[A[i]]);
}
}
for (int i = 0; i < n; i++)
if (A[i] != i)
return i + 1;
return n+1;
}
};
