c_cpp GFG第一个非重复元素

Posted 2021-05-14

#include <bits/stdc++.h>
using namespace std;

// #Maps #Hashing #GFG #Problem
// https://practice.geeksforgeeks.org/problems/non-repeating-element/0/?track=SP-Hashing

int firstNonRep(vector<int> a){
    map < int, int > count;
    for(int i=0;i<a.size();i++){
        count[a[i]]+=1;
    }
    for(int i=0;i<a.size();i++){
        if(count[a[i]]==1){
            return a[i];
        }
    }
    return 0; // if no such element exists
}

int main() {
	int t;
	cin>>t;
	while(t--){
	    int n;
	    cin>>n;
	    vector<int> a(n);
	    for(int i=0;i<n;i++){
	        cin>>a[i];
	    }
	    cout<<firstNonRep(a)<<endl;
	}
	return 0;
}