First Missing Positive
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.
通过swap操作，把各个元素swap到相应的位置上，然后再扫描一遍数组，确定丢失的正数的位置
class Solution {
public:
int firstMissingPositive(int A[], int n) {
if(n==) return ;
for(int i=;i<n;i++)
{
if(A[i]!=i+&&A[i]<=n&&A[i]>=&&A[i]!=A[A[i]-])
{
swap(A[i],A[A[i]-]);
i--;
}
}
for(int i=;i<n;i++)
{
if(A[i]!=i+) return i+;
}
return n+;
}
void swap(int &a,int &b)
{
int tmp=a;
a=b;
b=tmp;
}
};