Reverse Words in a String

Reverse Words in a String

反转一个字符串

垃圾方法：

#include <sstream>
#include <vector>

class Solution {
public:
    void reverseWords(string &s) {
        istringstream is(s);
        string word;
        vector<string> dict;
        while (is >> word) {
            dict.push_back(word);
        }
        string ret = "";
        for (int i = dict.size() - 1; i > 0; --i) {
            ret = ret + dict[i] + " ";
        }
        if (dict.size() > 0)
            ret += dict[0];
        s = ret;
    }
};

Evaluate Reverse Polish Notation

简单计算器

 

class Solution {
public:
    int evalRPN(vector<string> &tokens) {
        stack<int> s;
        for (int i = 0; i < tokens.size(); ++i) {
            if (tokens[i] != "+" && tokens[i] != "-" && tokens[i] != "*" && tokens[i] != "/") {
                s.push(s2i(tokens[i]));
            } else {
                int a = s.top();
                s.pop();
                int b = s.top();
                s.pop();
                if (tokens[i] == "-") s.push(b - a);
                if (tokens[i] == "+") s.push(b + a);
                if (tokens[i] == "*") s.push(b * a);
                if (tokens[i] == "/") s.push(b / a);
            }
        }
        return s.top();
    }
    
    int s2i(string &token) {
        bool sign = true;
        if (token[0] == '-') sign = false;
        int b = 1;
        int ret = 0;
        int end = sign ? 0 : 1;
        for (int i = token.size() - 1; i >= end; --i) {
            ret += b * (token[i] - '0');
            b *= 10;
        }
        return sign ? ret : (-ret);
    }
};