Java for LeetCode 227 Basic Calculator II
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
解题思路:
注意:测试中会出现“4*3/5”这样的情况,因此,可以用一个TempRes保存上一次运算的结果,TempOp表示距离本次运算符最近的+-运算符,具体看代码即可:
static public int calculate(String s) { int res = 0, tempRes = 0, Option = 1, tempOp = 1; for (int i = 0; i < s.length(); i++) { switch (s.charAt(i)) { case ' ': break; case '+': Option = 1; break; case '-': Option = -1; break; case '*': Option = 2; break; case '/': Option = 3; break; default: int num = 0; while (i < s.length() && Character.isDigit(s.charAt(i))) num = num * 10 + s.charAt(i++) - '0'; i--; switch (Option) { case 1: res += tempOp * tempRes; tempRes = num; tempOp = 1; break; case -1: res += tempOp * tempRes; tempRes = num; tempOp = -1; break; case 2: tempRes *= num; break; case 3: tempRes /= num; } } } res += tempOp * tempRes; return res; }