使用这种读入方式，MLE on #9，125MB

#include<bits/stdc++.h>
using namespace std;
string f() {
	char x = getchar();
	int k;
	string s = "", rip = "";
	while( x != '\n' ) {
		if( x == '[' ) {
			cin>> k;
			rip = f();
			while( k --> 0 ) 
				s += rip;
		}
		else if( x == ']' ) return s;
		else s += x;
		x = getchar();
	}
}
int main() {
	cout<< f();
	return 0;
}

然鹅，换成了这种，#9的内存空间变成了684KB?

#include<bits/stdc++.h>
using namespace std;
string f() {
	char x;
	int k;
	string s = "", rip = "";
	while( cin>> x ) {
		if( x == '[' ) {
			cin>> k;
			rip = f();
			while( k --> 0 ) 
				s += rip;
		}
		else if( x == ']' ) return s;
		else s += x;
	}
}
int main() {
	cout<< f();
	return 0;
}

萌新不知道为什么，求大佬解答