Leetcode:basic Calculator II

Basic Calculator II


Total Accepted: 23197 Total Submissions: 91345 Difficulty: Medium

Implement a basic calculator to evaluate a simple expression string.

The expression string contains onlynon-negativeIntegers,+,-,*,/Operators and empty Spaces.

The integer division should truncate toward zero.

Assume that the given expression was always valid.

Some Examples:

"3+2*2" = 7 "3/2" = 1 "3+5/2" = 5

Note: don't use the eval built-in library function.

Credits:
Special thanks to @ts for adding this problem and creating all test cases.

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Java code:

public class Solution {public int calculate (String s) {int len = s.length ();                if (S==null | | len==0) return 0;                stack<integer> stack = new stack<integer> ();        Char sign = ' + ';        int num = 0;            for (int i=0;i<len;i++) {char c = s.charat (i);                            if (Character.isdigit (c)) num = ten * num + c ' 0 '; if (! Character.isdigit (c) && c! = "| |                        i==len-1) {switch (sign) {case ' + ': Stack.push (num);                    Break                        Case '-': Stack.push (-num);                    Break                        Case ' * ': Stack.push (Stack.pop () *num);                    Break                Case '/': Stack.push (Stack.pop ()/num);                } sign = C;            num = 0;  }        }              int ans = 0;        for (int x:stack) ans + = x;    return ans; }}

Leetcode:basic Calculator II