#include<bits/stdc++.h>
using namespace std;
string a,b;
int main(){
	system("color F1");
	cin>>a;
	int t=a.size();
	for(int i=0;i<t;i++){
		if(a[i]=='A') b+='T';
		else if(a[i]=='T') b+='A';
		else if(a[i]=='G') b+='C';
		else if(a[i]=='C') b+='G';
	}
	cout<<b<<endl;
	return 0;
}

嘿兄弟怎么简单的题还来看题解？

#include <bits/stdc++.h>
using namespace std;
char s[2222222];
int main(){
	cin>>s;
	for(int i=0;i<strlen(s);i++){
		if (s[i]=='A') cout<<"T";
		else if (s[i]=='G') cout<<"C";
		else if (s[i]=='T') cout<<"A";
		else if (s[i]=='C') cout<<"G";
	}
	return 0;
}

竟然没有题解