LeetCode 1002: Find Common Characters Solution

Master LeetCode problem 1002 (Find Common Characters), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1002. Find Common Characters

Easy

Array Hash Table String

Problem Explanation

Explanation

To solve this problem, we can use a hashmap to keep track of the frequency of characters in each word. We initialize the hashmap using the characters and their frequencies from the first word. Then, for each subsequent word, we update the hashmap to keep only the common characters and their minimum frequencies across all words. Finally, we construct the result array by adding the common characters based on their minimum frequencies.

Algorithm:
1. Initialize an array commonChars with the frequencies of characters in the first word.
2. For each word in the input array:
  - Create a hashmap wordMap to store the frequencies of characters in the current word.
  - Update the commonChars array to keep only the common characters and their minimum frequencies.
3. Construct the result array by adding the common characters based on their minimum frequencies.
Time Complexity: O(n * m), where n is the number of words and m is the average length of a word.
Space Complexity: O(1) since the size of the hashmap is constant (26 lowercase English letters).

Solution Code

class Solution {
    public List<String> commonChars(String[] words) {
        List<String> result = new ArrayList<>();
        int[] commonChars = new int[26];

        for (char c : words[0].toCharArray()) {
            commonChars[c - 'a']++;
        }

        for (int i = 1; i < words.length; i++) {
            int[] wordMap = new int[26];
            for (char c : words[i].toCharArray()) {
                wordMap[c - 'a']++;
            }

            for (int j = 0; j < 26; j++) {
                commonChars[j] = Math.min(commonChars[j], wordMap[j]);
            }
        }

        for (int i = 0; i < 26; i++) {
            while (commonChars[i] > 0) {
                result.add(String.valueOf((char) (i + 'a')));
                commonChars[i]--;
            }
        }

        return result;
    }
}

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