1144 The Missing Number（20 分）

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

题意：给出n个数，输出不在给出的数中的最小正整数。
分析：1.用set去接收这些数（排序+去重）
题解：

#include<cstdlib>
#include<cstdio>
#include<set>
using namespace std;
int main() {
    int n;
    set<int> s;
    scanf("%d", &n);
    for (int i = 0; i != n; i++) {
        int t;
        scanf("%d", &t);
        s.insert(t);
    }
    int pre = *(s.begin());
    for (set<int>::iterator it = ++s.begin(); it != s.end(); it++) {
        if (*it - pre != 1 && pre+1 > 0) {
            printf("%d", pre + 1);
            return 0;
        }
        pre = *(it);
    }
    //如果遍历到最后一个仍然找不到符合要求的结果，
    //则输出最大的数之后的正整数（最大的数可能为正，或者仍为负）
    if (pre >= 0) {
        printf("%d", pre + 1);
    }
    else {
        printf("%d", 1);
    }
    return 0;
}