【王道机试笔记07】栈

栈

栈的标准模板库及其使用如下。

#include<stack>
stack<int> S;
S.push(i);
int x = S.top();
S.pop();

例3.1 括号匹配问题

代码3.1

#include<iostream>
#include<stack>
#include<string.h>
using namespace std;
int main(){
	stack<char> S;
	string buf;
	char ans[105];
	int i;
	while(cin >> buf){
		int max = buf.length();
		for(i=0;i<max;i++){
			if(buf[i] == '('){
				S.push(i);
				ans[i] = ' ';
			}
			else if(buf[i] == ')'){
				if(S.empty())
					ans[i] = '?';
				else{
					S.pop();
					ans[i] = ' ';
				}
			}
			else{
				ans[i] = ' ';
			}
		}
		int x;
		while(!S.empty()){
			x = S.top();
			S.pop();
			ans[x] = '$';
		}
		for(i=0;i<max;i++)
			cout << buf[i];
		cout << endl;
		for(i=0;i<max;i++)
			cout << ans[i];
		cout << endl;
	}
	return 0;
}

例3.2 简单计算器

代码3.2

#include<iostream>
#include<stack>
using namespace std;
char str[205];
int mat[][5] = {
	1,0,0,0,0,
	1,0,0,0,0,
	1,0,0,0,0,
	1,1,1,0,0,
	1,1,1,0,0
};
stack<int> op;
stack<double> in;
void getOp(bool &reto,int &retn,int &i){
	if(i == 0 && op.empty() == true){
		reto = true;
		retn = 0;
		return ;
	}
	if(str[i] == 0){
		reto = true;
		retn = 0;
		return ;
	}
	if(str[i] >= '0' && str[i] <= '9'){
		reto = false;
	}
	else{
		reto = true;
		if(str[i] == '+'){
			retn = 1;
		}
		else if(str[i] == '-'){
			retn = 2;
		}
		else if(str[i] == '*'){
			retn = 3;
		}
		else if(str[i] == '/'){
			retn = 4;
		}
		i += 2;
		return ;
	}
	retn = 0;
	for(;str[i] != ' ' && str[i] != 0;i++){
		retn *= 10;
		retn += str[i] - '0';
	}
	if(str[i] == ' ')
		i++;
	return;
}
int main(){
	while(gets(str)){
		if(str[0] == '0' && str[1] == 0)
			break;
		while(!op.empty())
			op.pop();
		while(!in.empty())
			in.pop();
		bool retop;
		int retnum;
		int idx = 0;
		while(true){
			getOp(retop,retnum,idx);
			if(retop == false){
				in.push((double)retnum);
			}
			else{
				double tmp;
				if(op.empty() == true || mat[retnum][op.top()] == 1)
					op.push(retnum);
				else{
					while(mat[retnum][op.top()] == 0){
						int ret = op.top();
						op.pop();
						double b = in.top();
						in.pop();
						double a = in.top();
						in.pop();
						if(ret == 1)
							tmp = a + b;
						else if(ret == 2)
							tmp = a - b;
						else if(ret == 3)
							tmp = a * b;
						else
							tmp = a / b;
						in.push(tmp);
					}
					op.push(retnum);
				}
			}
			if(op.size() == 2 && op.top() == 0)
				break;
		}
		printf("%.2f\n",in.top());
	}
	return 0;
}

堆栈的使用

#include<iostream>
#include<stack>
using namespace std;
stack<int> S;
int main(){
	int N;
	int num;
	char op;
	while(cin >> N){
		while(!S.empty())
			S.pop();
		while(N--){
			cin >> op;
			if(op == 'P'){
				cin >> num;
				S.push(num);
			}
			else if(op == 'O'){
				if(!S.empty())
					S.pop();
			}
			else if(op == 'A'){
				if(S.empty())
					cout << 'E' << endl;
				else
					cout << S.top() << endl;
			}
		}
		cout << endl;
	}
	return 0;
}

表达式求值

坑待填。