pta 1144 The Missing Number

Given N integers, you are supposed to find the smallest positive integer that is NOT in the given list.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤10​5​​). Then N integers are given in the next line, separated by spaces. All the numbers are in the range of int.

Output Specification:

Print in a line the smallest positive integer that is missing from the input list.

Sample Input:

10
5 -25 9 6 1 3 4 2 5 17

Sample Output:

7

题目大意：给定n个数，找出这n个数里丢失的最小的正整数

注意细节：

（1）可能n个数全是负数，输出1

（2）正整数要从1开始记录，数中可能存在重复的数

（3）可能n个数都是连续的正整数，且从1开始，那么输出最大的数+1

代码如下：

#include<bits/stdc++.h>
using namespace std;
int a[1000002];
int main()
{
	int n;
	while(cin >> n)
	{
		for(int i = 0;i < n;i ++)
		{
			cin >> a[i];
		}
		sort(a,a + n);
		int i,fl = 0;
		for(i = 0;i < n - 1;i ++)
		{
			if(a[i] > 0)
			{
				if(a[i] == 1)
				fl = 1;
				if(fl)
				{
					if(a[i] == a[i + 1] || a[i + 1] == a[i] + 1)
					continue;
					else
					{
						cout << a[i] + 1 << endl;
						break;
					}
				}
				else
				{
					cout << fl + 1 << endl;
					break;
				}
			}
		}
		if(i == n - 1)
		{
			if(a[n - 1] > 0)
			cout << a[n - 1] + 1 << endl;
			else
			cout << 1 << endl;
		}
	}
	return 0;
}