Basic Calculator Base Calculator-leetcode

1. Title:

Implement a basic calculator to evaluate a simple expression string.

The expression string may contain open ( and closing parentheses ) , the plus + or minus sign - , Non-negati ve integers and empty spaces .

Assume that the given expression was always valid.

Some Examples:

"1 + 1" = 2 "2-1 + 2" = 3 "(1+ (4+5+2)-3) + (6+8)" = 23

The title requirement is to implement a basic calculator that takes a string as input, implementing addition subtraction and parentheses. There are 0-9,+,-, (,) and white space symbols in the string.

You can assume that all calculations are non-negative. It can be considered that the input of the topic is a valid formula. There may be spaces in the string that you need to dispose of yourself.

2. Ideas:

Recursively calculates the value of each sub-sum minus.

What is a sub-formula? Think the whole equation is the first subtype. The first expression enclosed in parentheses is the second subtype. In turn.

For example

(1+ (4+5+2)-3) + (6+8)

, the first subtype is (1+ (4+5+2)-3) + (6+8). The second subtype is (1+ (4+5+2)-3). The third one is (4+5+2). The fourth one is (6+8).

So

A value that requires the first subtype is equal to the second subtype + fourth subtype.

A value of the second subtype is required, which is equal to the 1+ of the third subtype-3.

• So, first there is a function 1, which takes a pointer to the beginning of a certain subtype, and returns the value of that subtype.
• Second, a function 2 is used to convert a string of 1, 23 Ah, 84 AH and other strings into the corresponding numeric 1,23,84. If the character to be converted is ' (', it means that the content to be converted is a subtype, then it is treated with function 1.)

3. Code

Give a Java implementation:

public class solution{public int calculate (String s) {//This is the function 1 int ans=0;        int sign=1;            while (Location<s.length ()) {ans+= (helper (s) *sign);            if (Location>=s.length ()) break;                if (S.charat (location) = = ') ') {location++;            return ans;            } sign= (S.charat (location) = = '-')? -1:1;        Location+=1;    } return ans;        } private int location=0;//This is the pointer to the sub-position of the private int helper (String s) {//This is the function 2 int op=0; while (Location<s.length () && (Character.isdigit (s.charat) | |                 Character.isspacechar (S.charat (location))) {if (Character.isdigit (S.charat)) {op*=10;            op+= (S.charat (location)-' 0 ');        } location++;            } if (Location<s.length () &&s.charat (location) = = ' (') {location++;        return calculate (s);    } return op; }}

Basic Calculator Base Calculator-leetcode