# Sorting | 450 DSA | Love Babbar

Posted on Jan 1, 0001

### 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

##### 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