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

 没什么坑。

AC代码：

//include <bits/stdc++.h>
#include <set>
#include <map>
#include <cmath>
#include <queue>
#include <stack>
#include <time.h>
#include <string.h>
#include <vector>
#include <string>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <functional>
#define sdddd(x,y,z,k) scanf("%d%d%d%d", &x, &y, &z, &k)
#define sddd(x,y,z) scanf("%d%d%d", &x, &y, &z)
#define sdd(x,y) scanf("%d%d", &x, &y)
#define sd(x) scanf("%d", &x)
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define per(i,a,b) for(int i=a;i>=b;i--)
//#define mp Debug(x) printf("%d\n", &x);
#define pb push_back
#define ms(x, y) memset(x, y, sizeof x)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const ll MOD = 1046513837;
const int maxn = 1e5 + 50;
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3f;
//typedef vector<ll> vec;
//typedef vector<vec> mat;
template <class T>
inline bool scan_d(T &ret) {
	char c; int sgn;
	if (c = getchar(), c == EOF) return 0;
	while (c != '-' && (c<'0' || c>'9')) c = getchar();
	sgn = (c == '-') ? -1 : 1;
	ret = (c == '-') ? 0 : (c - '0');
	while (c = getchar(), c >= '0'&&c <= '9') ret = ret * 10 + (c - '0');
	ret *= sgn;
	return 1;
}

int arr[maxn];
int main() {
    int n;
    cin >> n;
    rep(i, 1, n){
        cin >> arr[i];
    }
    int isone = 1;
    rep(i, 1, n){
        if(arr[i] == 1){
            isone = 0;
        }
        if(arr[i] <= 0){
            arr[i] = 1;
        }
    }
    if(isone){
        cout << 1 << endl;
        return 0;
    }
    arr[n+1] = INF;
    rep(i, 1, n){
        if(abs(arr[i]) <= n){
            arr[abs(arr[i])] = -abs(arr[abs(arr[i])]);
        }
    }
    rep(i, 1, n+1){
        if(arr[i] > 0){
            cout << i << endl;
            return 0;
        }
    }
	return 0;
}

/*
HZH -> PRS -> ROM 195
HZH -> PKN -> GDN -> ROM 195
HZH -> BLN -> ROM 180
*/