1144 The Missing Number （20 分)

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

解题思路：这道题有个坑：数据范围在0~100000以内，但是注意题目这里出的有错误：For each case, the first line gives a positive integer N (≤10​^5​​). 题目明说给定的数据个数在1e5内，但是数据大小没有说在1e5以内，导致第一次提交出现段错误，我还以为是数组开的太小所致，还打算用二维数组做（并不能，没有别的办法了，数组并不能开到10位）

注：integer最大数据为一个十位数2147483647

测试点	结果	耗时	内存
0	答案正确	3 ms	592 KB
1	答案正确	2 ms	356 KB
2	答案正确	2 ms	396 KB
3	答案正确	2 ms	384 KB
4	答案正确	80 ms	384 KB
5	答案正确	71 ms	808 KB
6	段错误	3 ms	352 KB

#include <iostream>
#include <bits/stdc++.h>
using namespace std;

const int N = 1e5+5;
int a[N];

int main()
{
    int n,x;
    cin >> n;
    for(int i = 0; i < n; i++){
        cin >> x;
        if(x>0&&x<N) a[x] = 1;
    }
    for(int i = 1; i < N; i++){
        if(!a[i]){
            printf("%d",i);
            break;
        }
    }
    return 0;
}