[leetcode]227. Basic Calculator II -- JavaScript 代码

一时失言乱红尘 2022-09-25 08:25 169阅读 0赞

/** * @param {string} s * @return {number} */
    var calculate = function(s) { 
        s = s.replace(new RegExp(" ","g"),"");
        var len = s.length;
        if(len===0){
            return 0;
        }
        var stack = [];
        var ret = 0;
        var sign = 1;
        var isMul = 0;
        for(var i=0;i<len;i++){
            var n = s.charAt(i);
            if (!isNaN(parseInt(n))){
                var cur = parseInt(n);
                while(i+1<len && (!isNaN(parseInt(s.charAt(i+1))))){
                    cur = 10*cur + parseInt(s.charAt(++i));  
                }
                if(s.charAt(i+1)=="+"||s.charAt(i+1)=="-"||s.charAt(i+1)===""){
                    if(stack.length===0){
                        ret += sign*cur;
                    }else{
                        if(isMul==1){
                            cur = cur*stack.pop();
                        }else if(isMul==-1){
                            cur = Math.floor(stack.pop()/cur);
                        }
                        s_sign = stack.pop();
                        s_ret = stack.pop();
                        ret = s_ret+s_sign*cur;
                        isMul = 0;
                    }
                }else if(s.charAt(i+1)=="*"||s.charAt(i+1)=="/"){
                    if(isMul===0){
                        stack.push(ret);
                        stack.push(sign);
                        stack.push(cur);
                        ret = 0;
                        sigh = 1;
                    }else{  // 3+8*9/3
                        if(isMul==1){
                            cur = cur*stack.pop();
                            stack.push(cur);
                        }else if(isMul==-1){
                            cur = Math.floor(stack.pop()/cur);
                            stack.push(cur);
                        }
                    }
                }
            }else if(n=="+"){
                sign = 1;
                isMul = 0;
            }else if(n=="-"){
                sign = -1;
                isMul = 0;
            }else if(n=="*"){
                isMul = 1;
            }else if(n=="/"){
                isMul = -1;
            }
        }
        return ret;
    
    };

同题目Basic Calculator一样，这道题也是应用了栈来做的。  
难点在于需要考虑的很周全。