LeetCode之“字符串”：Length of Last Word & Reverse Words in a String

　　1. Length of Last Word

　　Given a string s consists of upper/lower-case alphabets and empty space characters ‘ ‘, return the length of last word in the string.

　　If the last word does not exist, return 0.

　　Note: A word is defined as a character sequence consists of non-space characters only.

　　For example, 
　　Given s = "Hello World",
　　return 5.

　　Solution:

class Solution {
public:
    int lengthOfLastWord(string s) {
        if(s.size() == 0)
            return 0;
        else
        {
            while(s.back() == ‘ ‘)
                s.pop_back();

            if(s.find(‘ ‘) == -1)
                return s.size();
            else
            {
                int len = 0;
                while(s.back() != ‘ ‘)
                {
                    len++;
                    s.pop_back();
                }
                return len;
            }
        }
    }
};

　　2. Reverse Words in a String

　　Given an input string, reverse the string word by word.

　　For example,
　　Given s = "the sky is blue",
　　return "blue is sky the".

　　Solution:

class Solution {
public:
    void reverse(string &s, int start, int end)
    {
        int sz = (end - start) / 2 + 1;
        for (int i = 0; i < sz; i++)
        {
            if (start + i != end - i)
            {
                char tmp = s[start + i];
                s[start + i] = s[end - i];
                s[end - i] = tmp;
            }
        }
    }

    void clearExtralSpace(string &s)
    {
        while (s.front() == ‘ ‘)
        {
            s.erase(0, 1);
        }
        while (s.back() == ‘ ‘)
        {
            s.pop_back();
        }
        int spacePos = s.find(‘ ‘);
        while (spacePos != -1)
        {
            while (s[spacePos + 1] == ‘ ‘)
            {
                s.erase(spacePos + 1, 1);
            }
            spacePos = s.find(‘ ‘, spacePos + 1);
        }
    }

    void reverseWords(string &s) {
        clearExtralSpace(s);
        if (s.size() > 1)
        {
            int isSpaceExist = s.find(‘ ‘);
            if (isSpaceExist != -1)
            {
                int szS = s.size();
                reverse(s, 0, s.size() - 1);
                int charPos = 0;
                int nextSpacePos = s.find(‘ ‘, charPos + 1);
                while (nextSpacePos != -1)
                {
                    reverse(s, charPos, nextSpacePos - 1);
                    charPos = nextSpacePos + 1;
                    nextSpacePos = s.find(‘ ‘, charPos + 1);
                }
                reverse(s, charPos, s.size() - 1);
            }
        }
    }
};