LeetCode227. 基本计算器 II

墨蓝 2022-11-07 05:46 154阅读 0赞

难度：`中等`

题目描述：

> 给你一个字符串表达式 s ，请你实现一个基本计算器来计算并返回它的值。
> 
> 整数除法仅保留整数部分。  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoYW9rdWRlenR0_size_16_color_FFFFFF_t_70]  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoYW9rdWRlenR0_size_16_color_FFFFFF_t_70 1]

class Solution { 
    public:
        int calculate(string s) { 
            int n=s.length();
            int i=0;
            long long num;
            long long ans=0;
            int sign=1;
            stack<int>cal;
            while(i<n){ 
                if(s[i]==' '){ 
                    i++;
                }else if(s[i]=='+'){ 
                    sign=1;
                    i++;
                }else if(s[i]=='-'){ 
                    sign=-1;
                    i++;
                }else if(s[i]=='*'){ 
                    i++;
                    while(s[i]==' '){ 
                        i++;
                    }
                    long long num1=0;
                    while(i<n&&s[i]>='0'&&s[i]<='9'){ 
                        num1=num1*10+s[i]-'0';
                        i++;
                    }
                    cal.top()=cal.top()*num1;
                }else if(s[i]=='/'){ 
                    i++;
                    while(s[i]==' '){ 
                        i++;
                    }
                    long long num1=0;
                    while(i<n&&s[i]>='0'&&s[i]<='9'){ 
                        num1=num1*10+s[i]-'0';
                        i++;
                    }
                    cal.top()=cal.top()/num1;
                }else{ 
                    num=0;
                    while(i<n&&s[i]>='0'&&s[i]<='9'){ 
                        num=num*10+s[i]-'0';
                        i++;
                    }
                    cal.push(num*sign);
                }
            }
            while(!cal.empty()){ 
                ans+=cal.top();
                cal.pop();
            }
            return ans;
        }
    };

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