LeetCode:Basic Calculator
Posted walker lee
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Basic Calculator
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.
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java code:
public class Solution { public int calculate(String s) { Stack<Integer> stack = new Stack<Integer>(); int result = 0; int sign = 1; int n = s.length(); for(int i=0;i<n;i++) { char c = s.charAt(i); if(Character.isDigit(c)) { int sum = c-'0'; while(i+1<n && Character.isDigit(s.charAt(i+1))) { sum = 10*sum + s.charAt(i+1)-'0'; i++; } result += sign * sum; } else if(c=='+') { sign = 1; } else if(c=='-') { sign = -1; } else if(c=='(') { stack.push(result); stack.push(sign); sign = 1; result = 0; } else if(c==')') { result = result * stack.pop() + stack.pop(); } } return result; } }
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