227. Basic Calculator II

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LeetCode

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class Solution {
    static int calculate(String s) {
        int len= s.length();
        if(s==null || len==0) return 0;
        LinkedList<Integer> stack = new LinkedList<Integer>();
        int num = 0;
        char sign = '+';
        for(int i=0;i<len;i++){
            char c = s.charAt(i);
            if(Character.isDigit(c)){
                num = num*10+c-'0';
            }
            if((!Character.isDigit(c) && c!=' ') || 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 = c;
                num = 0;
            }
        }
        int total = 0;
        while (!stack.isEmpty()) total += stack.pop();
        return total;
    }
}

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