标签：ssi equals ace cat style war color 运算 while
Implement a basic calculator to evaluate a simple expression string.
The expression string contains only non-negative integers, +, -, *, / operators and empty spaces . The integer division should truncate toward zero.
You may assume that the given expression is always valid.
Some examples:
"3+2*2" = 7 " 3/2 " = 1 " 3+5 / 2 " = 5
带有+、-、*、／的运算。
与上一题累死，用栈做。
public class Solution { public int calculate(String s) { Stack<String> stack = new Stack(); int start = 0; int num = 0; while (start < s.length()){ char ch = s.charAt(start); if (Character.isDigit(ch)){ num = num * 10 + ch - ‘0‘; } else if(ch == ‘ ‘ ){ } else { if (!stack.isEmpty() && (stack.peek().equals("*") || stack.peek().equals("/"))){ String str = stack.pop(); int num2 = Integer.valueOf(stack.pop()); if (str.equals("*")){ num = num2 * num; } else { num = num2 / num; } } stack.push(String.valueOf(num)); stack.push(String.valueOf(ch)); num = 0; } start++; } if (!stack.isEmpty() && (stack.peek().equals("*") || stack.peek().equals("/"))){ String str = stack.pop(); int num2 = Integer.valueOf(stack.pop()); if (str.equals("*")){ num = num * num2; } else { num = num2 / num; } } if (!stack.isEmpty() && stack.pop().equals("-")){ num = -num; } while (stack.size() > 1){ int num1 = Integer.valueOf(stack.pop()); if (stack.pop().equals("-")){ num1 = -num1; } num = num + num1; } if (!stack.isEmpty()) return Integer.valueOf(stack.pop()) + num; else { return num; } } }
public class Solution { public int calculate(String s) { int len; if(s==null || (len = s.length())==0) return 0; Stack<Integer> stack = new Stack<Integer>(); int num = 0; char sign = ‘+‘; for(int i=0;i<len;i++){ if(Character.isDigit(s.charAt(i))){ num = num*10+s.charAt(i)-‘0‘; } if((!Character.isDigit(s.charAt(i)) &&‘ ‘!=s.charAt(i)) || i==len-1){ if(sign==‘-‘){ stack.push(-num); } if(sign==‘+‘){ stack.push(num); } if(sign==‘*‘){ stack.push(stack.pop()*num); } if(sign==‘/‘){ stack.push(stack.pop()/num); } sign = s.charAt(i); num = 0; } } int re = 0; for(int i:stack){ re += i; } return re; } }
leetcode 227. Basic Calculator II ---------- java
标签：ssi equals ace cat style war color 运算 while
原文地址：http://www.cnblogs.com/xiaoba1203/p/7162044.html
