Accepted implementation for the problem 1208B in codeforces

codeforces-1208B.cpp

/*
 * =====================================================================================
 *
 *       Filename:  1208B.cpp
 *
 *    Description:  codeforces 1208B: Uniqueness
 *
 *        Version:  1.0
 *        Created:  2019年08月31日
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  lionking
 *   Organization:  None
 *
 * =====================================================================================
 */

// possible cases:
// case 1:
// 10
// 7 7 7 1 2 3 4 5 6 7
// answer: 3 (first 3 digits: 7 7 7)
//
// case 2:
// 10
// 1 2 3 4 3 4 5 6 7 1
// answer: 4 (first 4 digits: 1 2 3 4)
// 
// case 3:
// 9
// 1 9 2 9 0 1 5 5 3
// answer: 4 (digit sequence: 9 0 1 5)
//
// case 4:
// 3
// 1 2 3
// answer: 0 (no digit needs to be removed)
//
// case 5:
// 10
// 1 9 2 9 0 1 5 5 3 9
// answer: 6 (digit sequence: 9 2 9 0 1 5)

#include <cstdio>
#include <unordered_set>

using namespace std;

int main()
{
    constexpr int NUM_SIZE = 2001;
    int n, num[NUM_SIZE];
    unordered_set<int> exist;
    scanf("%d", &n);
    for (int i = 1; i <= n; ++i) {
        scanf("%d", num+i);
    }

    int lidx = 1;
    for (; (lidx <= n) && (exist.count(num[lidx]) == 0); ++lidx) {
        exist.emplace(num[lidx]);
    }

    auto result = n;
    int ridx = n;
    for (--lidx; lidx >= 0; --lidx) {
        for (; (ridx > 0) && (exist.count(num[ridx]) == 0); --ridx) {
            exist.emplace(num[ridx]);
        }
        result = min(result, ridx - lidx);
        exist.erase(num[lidx]);
    }
    printf("%d\n", result);
    
    return 0;
}