delete pics to save space

history_source/信息学奥赛一本通/2.1.3.cpp

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+#include<iostream>
+#include<string>
+using namespace std;
+void swap(string &a,string &b)
+{
+	string c;
+	c=a;
+	a=b;
+	b=c;
+}
+void eraseZero(string &a)
+{
+	while(a[0]=='0'&&a.size()>1) a.erase(0,1);
+}
+string add_(string a,string b)
+{
+	string c;
+	int ai,bi,j=0,x;
+	eraseZero(a);
+	eraseZero(b);
+	if(b.size()>a.size()) swap(a,b);
+	for(ai=a.size()-1,bi=b.size()-1;bi>=0;bi--,ai--)
+	{
+		x=j+a[ai]+b[bi]-2*'0';
+		c=char('0'+x%10)+c;
+		j=x/10;
+	}
+	while(ai>=0)
+	{
+		x=j+a[ai]-'0';
+		c=char('0'+x%10)+c;
+		j=x/10;
+		ai--;
+	}
+	if(j) c="1"+c;
+	eraseZero(c);
+	return c;
+}
+int main()
+{
+	string ans="1";
+	int n;
+	cin>>n;
+	for(int i=0;i<n;i++) ans=add_(ans,ans);
+	cout<<ans<<endl;
+	return 0;
+}