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//224. Basic Calculator My Submissions Question

//Total Accepted: 24957 Total Submissions: 115632 Difficulty: Medium

//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-negative integers and empty spaces .

//

//You may assume that the given expression is always valid.

//

//Some examples:

//"1 + 1" = 2

//" 2-1 + 2 " = 3

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

//Note: Do not use the eval built-in library function.

public class Solution {

public int calculate(String s) {

int len=s.length();

int sign=1;

int result=0;

Stack<Integer> stack=new Stack<Integer>();

int i,j;

int val;

int sum=0;

char ch;

for(i=0;i<len;i++)

{

ch=s.charAt(i);

if(Character.isDigit(ch))

{

sum=ch-'0';

while(i+1 < len && Character.isDigit(s.charAt(i+1)))

{

sum=(sum*10) + s.charAt(i+1)-'0';

i++;

}

result+=sign * sum;

}

else if(ch=='+')

{

sign=1;

}

else if(ch=='-')

{

sign=-1;

}

else if(ch=='(')

{

stack.push(result);

result=0;

stack.push(sign);

sign=1;

}

else if(ch==')')

{

result=result*stack.pop()+stack.pop();

}

}

return result;

}

}