[problem:1848A]↵
↵
Hello CF! Could you explain to me why these two codes output different results?↵
↵
### Problem 1848A: Vika and Her Friends↵
↵
#### My Code:↵
~~~~~↵
#include <iostream>↵
#include <vector>↵
using namespace std;↵
typedef long long ll;↵
↵
void solve() {↵
ll n, m, k; //Size of mall and # of Vika's friends↵
ll x, y; //Vika's coordinate↵
cin >> n >> m >> k >> x >> y;↵
↵
//For each of vika's friends, check whether they are in the same square as her. If so, print NO↵
for(int i = 0; i < k; i++) {↵
int xx, yy;↵
cin >> xx;↵
cin >> yy;↵
//!!! PROBLEM SEEMS TO BE HERE vvv!!!↵
if((x + y) % 2 == (xx + yy) % 2) { ↵
cout << "NO" << endl;↵
return;↵
}↵
}↵
cout << "YES" << endl;↵
//!!! PROBLEM SEEMS TO BE HERE ^^^!!!↵
}↵
↵
int main() {↵
int t;↵
cin >> t;↵
while(t--) {↵
solve();↵
}↵
}↵
~~~~~↵
↵
#### Editorial's code:↵
~~~~~↵
#include <bits/stdc++.h>↵
↵
using namespace std;↵
↵
#define int long long↵
↵
int32_t main() {↵
int t;↵
cin >> t;↵
while (t--) {↵
int n, m, k;↵
cin >> n >> m >> k;↵
int x, y;↵
cin >> x >> y;↵
string ans = "YES\n";↵
for (int i = 0; i < k; ++i) {↵
int xx, yy;↵
cin >> xx >> yy;↵
if ((x + y) % 2 == (xx + yy) % 2) {↵
ans = "NO\n";↵
}↵
}↵
cout << ans;↵
}↵
return 0;↵
}↵
~~~~~↵
↵
The problem seems to be inside the for-loop. I used a different method to output a "NO" when it's found that one of Vika's friend is on the same square colour as Vika. This method seems to yield an incorrect result when there's a previous test case ('t') that outputs a 'NO' already (although I could be wrong).↵
↵
I asked ChatGPT several times with different prompts on why these two code output different results, but I'm still quite confused. Out of options, I have to resort to asking you guys. Would be really nice if you guys could help a little newbie like me. Thanks!↵
↵
↵
↵
#### **EDIT: MISTAKE FOUND** by Hazzler. Thank you for your time!↵
By using the return function, I didn't finish reading all the input from testcases that yields a NO before moving on to the next testcase. The result is the rest of the input from this testcase will be read as an input for the next testcase, leading to an incorrect result.↵
↵
In hindsight, this mistake is one of the 200 IQ moments of all time.↵
↵
Hello CF! Could you explain to me why these two codes output different results?↵
↵
### Problem 1848A: Vika and Her Friends↵
↵
#### My Code:↵
~~~~~↵
#include <iostream>↵
#include <vector>↵
using namespace std;↵
typedef long long ll;↵
↵
void solve() {↵
ll n, m, k; //Size of mall and # of Vika's friends↵
ll x, y; //Vika's coordinate↵
cin >> n >> m >> k >> x >> y;↵
↵
//For each of vika's friends, check whether they are in the same square as her. If so, print NO↵
for(int i = 0; i < k; i++) {↵
int xx, yy;↵
cin >> xx;↵
cin >> yy;↵
//!!! PROBLEM SEEMS TO BE HERE vvv!!!↵
if((x + y) % 2 == (xx + yy) % 2) { ↵
cout << "NO" << endl;↵
return;↵
}↵
}↵
cout << "YES" << endl;↵
//!!! PROBLEM SEEMS TO BE HERE ^^^!!!↵
}↵
↵
int main() {↵
int t;↵
cin >> t;↵
while(t--) {↵
solve();↵
}↵
}↵
~~~~~↵
↵
#### Editorial's code:↵
~~~~~↵
#include <bits/stdc++.h>↵
↵
using namespace std;↵
↵
#define int long long↵
↵
int32_t main() {↵
int t;↵
cin >> t;↵
while (t--) {↵
int n, m, k;↵
cin >> n >> m >> k;↵
int x, y;↵
cin >> x >> y;↵
string ans = "YES\n";↵
for (int i = 0; i < k; ++i) {↵
int xx, yy;↵
cin >> xx >> yy;↵
if ((x + y) % 2 == (xx + yy) % 2) {↵
ans = "NO\n";↵
}↵
}↵
cout << ans;↵
}↵
return 0;↵
}↵
~~~~~↵
↵
The problem seems to be inside the for-loop. I used a different method to output a "NO" when it's found that one of Vika's friend is on the same square colour as Vika. This method seems to yield an incorrect result when there's a previous test case ('t') that outputs a 'NO' already (although I could be wrong).↵
↵
I asked ChatGPT several times with different prompts on why these two code output different results, but I'm still quite confused. Out of options, I have to resort to asking you guys. Would be really nice if you guys could help a little newbie like me. Thanks!↵
↵
↵
↵
#### **EDIT: MISTAKE FOUND** by Hazzler. Thank you for your time!↵
By using the return function, I didn't finish reading all the input from testcases that yields a NO before moving on to the next testcase. The result is the rest of the input from this testcase will be read as an input for the next testcase, leading to an incorrect result.↵
↵
In hindsight, this mistake is one of the 200 IQ moments of all time.↵
