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:
1
2
Input: [1,2,3,3]
Output: 3
Example 2:
1
2
Input: [2,1,2,5,3,2]
Output: 2
Example 3:
1
2
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).
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
#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;
}