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## Discussion of Problem 1737. Mnemonics and Palindromes 3

TLE with G++ 4.9, AC with Visual C++ 2013
Posted by zlo 26 Jul 2017 16:53
For some reason I get TLE with G++ 4.9 and AC with Visual C++ 2013 with exactly the same code. I tried to use scanf/printf instead of cin/cout, but had no difference. On my machine this code works <100ms for every n with G++. Can anyone explain why I get TLE with G++? Thanks!

#include <string>
#include <queue>
#include <iostream>

using namespace std;

int main() {
int n;
cin >> n;
queue<string> result;
result.push("a");
result.push("b");
result.push("c");
char abc[] = {'a', 'b', 'c'};
for (int i = 1; i < n; i++) {
while (true) {
string &s = result.front();
if (s.size() > i) {
break;
}
char last = s[s.size() - 1];
if (s.size() > 1) {
char lbo = s[s.size() - 2];
for (int k = 0; k < 3; k++) {
char c = abc[k];
if (last != c && lbo != c) {
result.push(s + c);
}
}
} else {
for (int k = 0; k < 3; k++) {
char c = abc[k];
if (last != c) {
result.push(s + c);
}
}
}
result.pop();
}
if ((i + 1) * result.size() > 100000) {
cout << "TOO LONG";
return 0;
}
}
while (!result.empty()) {
cout << result.front() << endl;
result.pop();
}
return 0;
}
Re: TLE with G++ 4.9, AC with Visual C++ 2013
Posted by Mahilewets 26 Jul 2017 17:17
Because s+c is a temporary object
You are creating temporary objects and throwing them away O(N)  times

Looks like G++ failed to notice that it is unnecessary to create and destroy objects

And MSVC noticed that and replaced with something more effective