Sword finger offer Second Edition: string (simple)

The finger of the sword Offer 05. Replace blank space

Please implement a function , Put the string s Replace each space in with "%20".

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

Example ：

Input ：s = “We are happy.”
Output ：“We%20are%20happy.”

Answer key

class Solution {
    
public:
    string replaceSpace(string s) {
    
        if (s.empty()) {
    
            return s;
        }

        string ans;

        for (char c : s) {
    
            if (c == ' ') {
    
                ans.push_back('%');
                ans.push_back('2');
                ans.push_back('0');
            }
            else {
    
                ans.push_back(c);
            }
        }
        
        return ans;
    }
};

The finger of the sword Offer 58 - II. Left rotation string

The left rotation operation of string is to transfer several characters in front of string to the end of string . Please define a function to implement the left rotation operation of string . such as , Input string "abcdefg" And number 2, This function will return the result of rotating two bits to the left "cdefgab".

Original link ： The finger of the sword Offer 58 - II. Left rotation string

Answer key

Local inversion + Global inversion

Time complexity O(N)
Spatial complexity O(1)

class Solution {
    
public:
    string reverseLeftWords(string s, int n) {
    
        if (s.empty()) return s;

        reverse(s.begin(), s.begin() + n);
        reverse(s.begin() + n, s.end());
        reverse(s.begin(), s.end());

        return s;
    }
};

String traversal

Time complexity O(N)
Spatial complexity O(N)

class Solution {
    
public:
    string moveLeft(string s, int left) {
    
        string ans = "";
        for (int i = 0; i < s.length(); ++i) {
    
            ans += s[(i + left) % s.length()];
        }
        
        return ans;
    }

    string reverseLeftWords(string s, int n) {
    
        if (s.empty()) return s;

        int left = n % s.length();
        if (left == 0) return s;
        else return moveLeft(s, left);
    }
};