2351. First Letter to Appear Twice LeetCode Solution

In this guide, you will get 2351. First Letter to Appear Twice LeetCode Solution with the best time and space complexity. The solution to First Letter to Appear Twice problem is provided in various programming languages like C++, Java, and Python. This will be helpful for you if you are preparing for placements, hackathons, interviews, or practice purposes. The solutions provided here are very easy to follow and include detailed explanations.

Table of Contents

  1. Problem Statement
  2. Complexity Analysis
  3. First Letter to Appear Twice solution in C++
  4. First Letter to Appear Twice solution in Java
  5. First Letter to Appear Twice solution in Python
  6. Additional Resources
2351. First Letter to Appear Twice LeetCode Solution image

Problem Statement of First Letter to Appear Twice

Given a string s consisting of lowercase English letters, return the first letter to appear twice.
Note:

A letter a appears twice before another letter b if the second occurrence of a is before the second occurrence of b.
s will contain at least one letter that appears twice.

Example 1:

Input: s = “abccbaacz”
Output: “c”
Explanation:
The letter ‘a’ appears on the indexes 0, 5 and 6.
The letter ‘b’ appears on the indexes 1 and 4.
The letter ‘c’ appears on the indexes 2, 3 and 7.
The letter ‘z’ appears on the index 8.
The letter ‘c’ is the first letter to appear twice, because out of all the letters the index of its second occurrence is the smallest.

Example 2:

Input: s = “abcdd”
Output: “d”
Explanation:
The only letter that appears twice is ‘d’ so we return ‘d’.

Constraints:

2 <= s.length <= 100
s consists of lowercase English letters.
s has at least one repeated letter.

See also  3180. Maximum Total Reward Using Operations I LeetCode Solution

Complexity Analysis

  • Time Complexity: O(n)
  • Space Complexity: O(26) = O(1)

2351. First Letter to Appear Twice LeetCode Solution in C++

class Solution {
 public:
  char repeatedCharacter(string s) {
    vector<bool> seen(26);

    for (const char c : s) {
      if (seen[c - 'a'])
        return c;
      seen[c - 'a'] = true;
    }

    throw;
  }
};
/* code provided by PROGIEZ */

2351. First Letter to Appear Twice LeetCode Solution in Java

class Solution {
  public char repeatedCharacter(String s) {
    boolean[] seen = new boolean[26];

    for (final char c : s.toCharArray()) {
      if (seen[c - 'a'])
        return c;
      seen[c - 'a'] = true;
    }

    throw new IllegalArgumentException();
  }
}
// code provided by PROGIEZ

2351. First Letter to Appear Twice LeetCode Solution in Python

class Solution:
  def repeatedCharacter(self, s: str) -> str:
    seen = [False] * 26

    for c in s:
      if seen[ord(c) - ord('a')]:
        return c
      seen[ord(c) - ord('a')] = True
 # code by PROGIEZ

Additional Resources

Happy Coding! Keep following PROGIEZ for more updates and solutions.

Similar: