g2301_2400.s2351_first_letter_to_appear_twice.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g2301_2400.s2351_first_letter_to_appear_twice;

// #Easy #String #Hash_Table #Counting #2022_08_14_Time_0_ms_(100.00%)_Space_42.3_MB_(29.00%)

/**
 * 2351 - First Letter to Appear Twice\.
 *
 * Easy
 *
 * 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.
**/
public class Solution {
    public char repeatedCharacter(String s) {
        int n = s.length();
        int[] hm = new int[26];
        for (int i = 0; i < n; i++) {
            char c = s.charAt(i);
            hm[c - 'a']++;
            if (hm[c - 'a'] > 1) {
                return c;
            }
        }
        return '0';
    }
}