遞迴

P-1-1. 合成函數(1)

#include<bits/stdc++.h>
using namespace std;

int eval(){
	string s;
	cin >> s;
	if(s[0]=='f'){
		int x = eval();
		return 2*x-1;
	}else if(s[0]=='g'){
		int x = eval();
		int y = eval();
		return x+2*y-3;
	}else{
		return stoi(s);
	}
}

int main(){
	cout << eval() << endl;
}

Q-1-2. 合成函數(2)

#include<bits/stdc++.h>
using namespace std;

int eval(){
	string s;
	cin >> s;
	if(s[0]=='f'){
		int x = eval();
		return 2*x-3;
	}else if(s[0]=='g'){
		int x = eval();
		int y = eval();
		return 2*x+y-7;
	}else if(s[0]=='h'){
		int x = eval();
		int y = eval();
		int z = eval();
		return 3*x-2*y+z;
	}else{
		return stoi(s);
	}
}

int main(){
	cout << eval() << endl;
}

P-1-3. 棍子中點切割

#include<bits/stdc++.h>
using namespace std;

pair<int,int> FIND(vector<int>&arr,int target){
	int l = 0;
	int r = arr.size()-1;
	int m = l+(r-l)/2;
	while(l<=r){
		m = l+(r-l)/2;
		if(arr[m]<target){
			l=m+1;
		}
		if(arr[m]==target){
			return {true,m};
		}
		if(arr[m]>target){
			r=m-1;
		}
	}
	return {false,l};
}

int cut(vector<int>&arr,int left,int right){
	if (right-left<=1) return 0;
	int m = FIND(arr,(arr[left]+arr[right])/2).second;
	cout << m << endl;
	return arr[right]-arr[left]+cut(arr,left,m)+cut(arr,m,right);
}

int main(){
	int n,l;cin >> n >> l;
	vector<int>v(n+2);
	v[0]=0;
	for(int i=1;i<=n;++i){
		cin >> v[i];
	}
	v[n+1]=l;
	cout << cut(v,0,n+1) << endl;
}