Sorting | 450 DSA | Love Babbar

Day 1

Problem 1: Reverse a string

• Write a function that reverses a string. The input string is given as an array of characters s.
• Leetcode

Worst/ Better

• Loop through the string from the back and store the elements in a new string.
• Time Complexity : O(n)
• Space Complexity : O(n)

Optimal

• Make two pointers pointing towards the extreme ends and swap till the front < rear.
• Time Complexity : O(n)
• Space Complexity : O(1)

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

Problem 2: Check for palindrome

• Given a string S, check if it is palindrome or not.
• Geeks For Geeks

Worst/ Better/Optimal

• Make two pointers pointing towards the extreme ends and check if ch[front] == ch[rear] till the front < rear.
• Time Complexity : O(n)
• Space Complexity : O(1)

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

Problem 3: Print duplicates in a string

• Print all the duplicates in the input string.

Worst/Better/Optimal

• Either create a hash-array or a hash-map.
• Time Complexity : O(n)
• Space Complexity : O(k) size of the map

Problem 4: Subjective

• Why String is Immutable or Final in Java
• Stack Overflow