Huge runtime difference in recursion involving strings in G++11 vs G++14

Правка en1, от Vicennial, 2017-03-15 12:20:01

I had to use recursion+strings for a problem in a contest and I stumbled upon this irregularity.

Sample Code 'A' with strings:

#include<bits/stdc++.h>
using namespace std;
int n;
void go(string s,int x){
	if(x>n) return;
	string p="1";
	s+=p;
	for(int i=0;i<20;i++){
		go(s,x+1);
	}	
}
int main(){
	cin>>n;
	string s="1";
	for(int i=0;i<20;i++){
		go(s,1);
	}
}

Using input=5
Results:
G++ 11 5.1.0 = 7987 ms, 2044 KB
G++ 14 6.2.0 = 889 ms, 1856 KB
------------------------------------

Sample Code 'B' without strings:

#include<bits/stdc++.h>
using namespace std;
int n;
void go(int s,int x){
	if(x>n) return;
	for(int i=0;i<20;i++){
		go(1,x+1);
	}	
}
int main(){
	cin>>n;
	for(int i=0;i<20;i++){
		go(1,1);
	}
}

Using input=6
Results:
G++ 11 5.1.0 = 3026 ms, 2012 KB
G++ 14 6.2.0 = 2995 ms, 1868 KB

To test it yourself, head over to http://codeforces.com/problemset/customtest

Why is there such a huge difference when strings are used?