401 string (344. reverse string, 541. reverse string II, Title: Sword finger offer 05. replace spaces, 151. reverse words in string)

344. Reverse string

class Solution {
    
public:
    void reverseString(vector<char>& s) {
    
        for (int i = 0, j = s.size() - 1; i < s.size() / 2; i++, j--)
        {
    
            s[i] ^= s[j];
            s[j] ^= s[i];
            s[i] ^= s[j];
        }
    }
};

541. Reverse string II

class Solution {
    
public:
    string reverseStr(string s, int k) {
    
        for(int i = 0; i < s.size(); i += (2*k))
        {
    
            if(i + k <= s.size())
            {
    
                reverse(s.begin()+i, s.begin()+i+k);
                continue;
            }

            reverse(s.begin()+i,s.end());
        }
        return s;
    }
};

subject ： The finger of the sword Offer 05. Replace blank space

class Solution {
    
public:
    string replaceSpace(string s) {
    
        int old_size = s.size();

        int blank_count = 0;
        for (int i = 0; i < old_size; i++)
        {
    
            if (s[i] == ' ')
            {
    
                blank_count++;
            }
        }

        s.resize(old_size + 2 * blank_count);

        int new_size = s.size();

        for (int i = new_size - 1, j = old_size - 1; i > j ; i--, j--)
        {
    
            if (s[j] != ' ')
            {
    
                s[i] = s[j];
            }
            else
            {
    
                s[i] = '0';
                s[i - 1] = '2';
                s[i - 2] = '%';
                i -= 2;
            }
        }
        return s;
    }
};

151. Invert words in string