标签：new pac for empty ace tor har cti examples
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.
分析：
one pass
1. curNum 存目前的值
2. 遇到 ＋ － ， res ＋＝ curNum ＊ sign ， sign 存＋－
3.有（）用一个stack存目前的res 和sign；
// res curNum 0 - 9 ; 10 -... public class Solution { public int calculate(String s) { if(s == null || s.length() == 0){ return 0; } Stack<Integer> stack = new Stack<>(); int res = 0; int curNum = 0; int sign = 1; for(int i = 0 ; i < s.length(); i++){ char temp = s.charAt(i); if(temp == ‘ ‘) continue; else if(Character.isDigit(temp)) curNum = curNum * 10 + (int) (temp - ‘0‘); else if( temp == ‘+‘){ res += sign * curNum; curNum = 0; sign = 1; } else if(temp == ‘-‘){ res += sign * curNum; curNum = 0; sign = -1; //prepare for (); } else if(temp == ‘(‘){ stack.push(res); stack.push(sign); res = 0; curNum = 0; sign = 1; } else if(temp == ‘)‘){ res += curNum * sign; if(!stack.isEmpty()) sign = stack.pop(); if(!stack.isEmpty()) res = res * sign + stack.pop(); curNum = 0; sign = 1; } } if(curNum != 0) res += curNum * sign; return res; } }
标签：new pac for empty ace tor har cti examples
原文地址：http://www.cnblogs.com/joannacode/p/6120496.html
