N-Repeated Element In Size 2N Array Problem


Description

LeetCode Problem 961.

In a array A of size 2N, there are N+1 unique elements, and exactly one of these elements is repeated N times.

Return the element repeated N times.

Example 1:

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Input: [1,2,3,3]
Output: 3

Example 2:

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Input: [2,1,2,5,3,2]
Output: 2

Example 3:

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Input: [5,1,5,2,5,3,5,4]
Output: 5


Sample C++ Code

This is a C++ solution using a hash table. The time complexity is O(n), and the space complexity is O(n).

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#include <iostream>
#include <vector>
#include <map>
#include <algorithm>

using namespace std;

int repeatedNTimes(vector<int>& A) {
    int len = A.size();
    int n = len / 2;
    map<int, int> ht;
    for (int i = 0; i < len; i ++) {
        if (ht.find(A[i]) == ht.end())
            ht[A[i]] = 0;
        ht[A[i]] ++;
        if (ht[A[i]] > 1)
            return A[i];
    }
    return ht[A[len-1]];
}

int main() {
    vector<int> A = {1, 2, 3, 3};
    cout << repeatedNTimes(A) << endl;
}




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