227. Basic Calculator II

最新推荐文章于 2022-08-29 13:11:23 发布

转载最新推荐文章于 2022-08-29 13:11:23 发布 · 64 阅读

0 ·

CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/joannacode/p/6120691.html

本文介绍了一个简单的表达式计算器实现，该计算器能够解析并计算包含加减乘除运算及空格的非负整数表达式。文章通过使用栈来辅助计算过程，并提供了具体的代码示例。

Implement a basic calculator to evaluate a simple expression string.

The expression string contains only non-negative integers, +, -, *, / operators and empty spaces . The integer division should truncate toward zero.

You may assume that the given expression is always valid.

Some examples:

"3+2*2" = 7
" 3/2 " = 1
" 3+5 / 2 " = 5

// put all the number into stack 
// if + num -> stack
// if - -num -> stack
// if *,/ pop()/num
public class Solution {
    public int calculate(String s) {
        if(s == null || s.length()== 0) return 0;
        int res = 0;
        int curNum = 0;
        char sign = '+';
        Stack<Integer> stack = new Stack<>();
        for(int i = 0 ; i < s.length(); i++){
            char temp = s.charAt(i);
            if(temp == ' ') continue;
            else if(Character.isDigit(temp)){
                curNum = curNum * 10 + temp - '0';
            }
            else if(temp == '+'){
                stack.push(operation(sign, curNum, stack));
                curNum = 0;
                sign = '+';
            }
            else if(temp == '-'){
                stack.push(operation(sign, curNum, stack));
                curNum = 0;
                sign = '-';
            }
            else if(temp == '*'){
                stack.push(operation(sign, curNum, stack));
                curNum = 0;
                sign = '*';
            }
             else if(temp == '/'){
                stack.push(operation(sign, curNum, stack));
                curNum = 0;
                sign = '/';
            }
        }
        res = operation(sign, curNum, stack);
        while(!stack.isEmpty()){
            res += stack.pop();
        }
        return res;
        
    }
    
    public int operation(char sign, int number, Stack<Integer> stack){
        if(sign == '+')
            return number;
        else if(sign == '-')
            return -number;
        else if(sign == '*'){
            if(!stack.isEmpty())
                return stack.pop() * number;
        }
        else if(sign == '/'){
            if(!stack.isEmpty())
                return stack.pop() / number;
        }
        return number;    
    }
}

转载于:https://www.cnblogs.com/joannacode/p/6120691.html