PAT A1144 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

 

#include <stdio.h>
#include <algorithm>
#include <limits.h>
#include <set>
using namespace std;
int main() {
    int n;
    scanf("%d", &n);
    set<int> st;
    for (int i = 0; i < n; i++) {
        int tmp;
        scanf("%d", &tmp);
        if (tmp > 0) {
            st.insert(tmp);
        }
    }
    int j = 1;
    for (auto it = st.begin(); it != st.end(); it++) {
        if (*it > j) {
            printf("%d", j);
            break;
        }
        else j++;
    }
    if(j==st.size()+1)printf("%d",j);
}

注意点：这里只保证了输入数不超过int大小，用hash不好做，不如直接用set，自动升序排列，找到第一个不满足的数。

第二个坑是测试点2-5都是输入数据连续的，缺失的是输入数据后面那个数