Basic Calculator II

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该题和前面的"

Basic Calculator

"的处理方法一样，只是加入了对"*"、"/"两种运算的支持。

class Solution {public:    bool isnum(char c){        if(c >= '0' && c <= '9')            return true;        return false;    }    int calculate(string s) {                vector<string> postorder;        stack<char> ccache;        stack<int> icache;        string tmp;        if(s.length() < 1)            return 0;//构造后缀表达式        for(int i = 0; i < s.length(); ){            if(s[i] == ' '){                i++;                continue;            }            if(!isnum(s[i])){                if(s[i] == '(' || ccache.empty()){                    ccache.push(s[i]);                    i++;                    continue;                }                if(s[i] == ')'){                    while(ccache.top() != '('){                        tmp = "";                        tmp += ccache.top();                        postorder.push_back(tmp);                        ccache.pop();                    }                    ccache.pop();                    i++;                    continue;                }                if(s[i] == '+' || s[i] == '-'){                    while(!ccache.empty() && ccache.top() != '(' ){                        tmp = "";                        tmp += ccache.top();                        postorder.push_back(tmp);                        ccache.pop();                    }                    ccache.push(s[i]);                    i++;                    continue;                }                if(s[i] == '*' || s[i] == '/'){                    while(!ccache.empty() && ccache.top() != '(' && ccache.top() != '+' && ccache.top() != '-'){                        tmp = "";                        tmp += ccache.top();                        postorder.push_back(tmp);                        ccache.pop();                    }                    ccache.push(s[i]);                    i++;                    continue;                }            }else{                int j = i;                while(j < s.length() && isnum(s[j]))                    j++;                tmp = "";                tmp = s.substr(i, j - i);                postorder.push_back(tmp);                i = j;            }        }//添加所有剩余的元素        while(!ccache.empty()){            tmp = "";            tmp += ccache.top();            ccache.pop();            postorder.push_back(tmp);        }

//通过后缀表达式计算结果值            int fir, sec, result;            for(int i = 0; i < postorder.size(); i++){                if(postorder[i] == "+" || postorder[i] == "-" || postorder[i] == "*" || postorder[i] == "/"){                    sec = icache.top();                    icache.pop();                    fir = icache.top();                    icache.pop();                                        if(postorder[i] == "+")                        result = fir + sec;                    if(postorder[i] == "-")                        result = fir - sec;                    if(postorder[i] == "*")                        result = fir * sec;                    if(postorder[i] == "/")                        result = fir / sec;                                        icache.push(result);                }else{                    icache.push(atoi(postorder[i].c_str()));                }            }            return icache.top();    }};

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