Missing number in array

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/// Raihan Ruhin (username : raihanruhin) /// Online resume: https://raihanruhin.github.io #include<bits/stdc++.h> using namespace std; #define SET(a) memset(a,-1,sizeof(a)) #define CLR(a) memset(a,0,sizeof(a)) #define PI acos(-1.0) #define MOD 1000000007 #define MX 100010 int main() { ios_base::sync_with_stdio(0), cin.tie(0); int tc, n, x; map<int, bool>mp; cin>>tc; while(tc--) { cin>>n; for(int i=1; i<n; i++) { cin>>x; mp[x]=true; } for(int i=1; i<=n; i++) if(!mp[i]) { cout<< i <<endl; break; } mp.clear(); } return 0; }