Calculator (force buckle)

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title: Calculator
date: 2022-04-18 15:15:13
tags: Make a little progress every day

---

Daily topic

subject ： Calculator

Given an integer containing a positive integer 、 Add (+)、 reduce (-)、 ride (*)、 except (/) Arithmetic expression of ( Except brackets ), Calculate the result .

The expression contains only non negative integers ,+, - ,*,/ Four operators and spaces . Division of integers preserves only the integral part .

Example ：

Example 1:

Input : “3+2*2”
Output : 7

Example 2:

Input : " 3/2 "
Output : 1

Example 3:

Input : " 3+5 / 2 "
Output : 5

explain ：

You can assume that the given expressions are valid .
Please do not use built-in library functions eval.

Small pit , There are spaces in the string , Need to replace

Code ：

class Solution {    public int calculate(String s) {        s =s.replaceAll(" ","");        Deque<Integer> stack = new ArrayDeque<>();        // First add the first one         char flag = '+';        // Initial value of the number         int num = 0;        for(int i=0;i<s.length();i++){            // Convert to numbers             if(Character.isDigit(s.charAt(i))){                num = num*10+s.charAt(i)-'0';            }            // Run according to the symbol , Namely * and /, High priority , First take out the numbers in the stack , Put it in after calculation             if(!Character.isDigit(s.charAt(i)) || i==s.length()-1){                if(flag=='+'){                    stack.push(num);                }else if(flag=='-'){                    stack.push(-num);                }else if(flag=='*'){                    stack.push(stack.pop()*num);                }else if(flag=='/'){                    stack.push(stack.pop()/num);                }                flag = s.charAt(i);                num =0;            }        }        // Traversal stack , Cumulative results         int res =0;        while(!stack.isEmpty()){            res += stack.pop();        }        return res;    }}

That's all about the calculator

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