Improved task 2351.

Author: javadev

README.md

@@ -1860,7 +1860,7 @@ implementation 'com.github.javadev:leetcode-in-java:1.12'
 | 2354 |[Number of Excellent Pairs](src/main/java/g2301_2400/s2354_number_of_excellent_pairs/Solution.java)| Hard | Array, Hash_Table, Binary_Search, Bit_Manipulation | 80 | 86.77
 | 2353 |[Design a Food Rating System](src/main/java/g2301_2400/s2353_design_a_food_rating_system/FoodRatings.java)| Medium | Hash_Table, Design, Heap_Priority_Queue, Ordered_Set | 364 | 83.35
 | 2352 |[Equal Row and Column Pairs](src/main/java/g2301_2400/s2352_equal_row_and_column_pairs/Solution.java)| Medium | Array, Hash_Table, Matrix, Simulation | 7 | 98.94
-| 2351 |[First Letter to Appear Twice](src/main/java/g2301_2400/s2351_first_letter_to_appear_twice/Solution.java)| Easy | Hash_Table, String, Counting | 1 | 63.38
+| 2351 |[First Letter to Appear Twice](src/main/java/g2301_2400/s2351_first_letter_to_appear_twice/Solution.java)| Easy | Hash_Table, String, Counting | 0 | 100.00
 | 2350 |[Shortest Impossible Sequence of Rolls](src/main/java/g2301_2400/s2350_shortest_impossible_sequence_of_rolls/Solution.java)| Hard | Array, Hash_Table, Greedy | 12 | 87.73
 | 2349 |[Design a Number Container System](src/main/java/g2301_2400/s2349_design_a_number_container_system/NumberContainers.java)| Medium | Hash_Table, Design, Heap_Priority_Queue, Ordered_Set | 208 | 54.57
 | 2348 |[Number of Zero-Filled Subarrays](src/main/java/g2301_2400/s2348_number_of_zero_filled_subarrays/Solution.java)| Medium | Array, Math | 3 | 99.90

src/main/java/g2301_2400/s2351_first_letter_to_appear_twice/Solution.java

@@ -1,21 +1,18 @@
 package g2301_2400.s2351_first_letter_to_appear_twice;
 
-// #Easy #Hash_Table #String #Counting #2022_08_07_Time_1_ms_(63.38%)_Space_41.7_MB_(82.50%)
-
-import java.util.HashMap;
+// #Easy #Hash_Table #String #Counting #2022_08_14_Time_0_ms_(100.00%)_Space_42.3_MB_(29.00%)
 
 public class Solution {
     public char repeatedCharacter(String s) {
-        HashMap<Character, Integer> map = new HashMap<>();
-        for (int i = 0; i < s.length(); i++) {
-            if (map.containsKey(s.charAt(i))) {
-                if (map.get(s.charAt(i)) >= 1) {
-                    return s.charAt(i);
-                }
-            } else {
-                map.put(s.charAt(i), map.getOrDefault(s.charAt(i), 0) + 1);
+        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 'c';
+        return '0';
     }
 }

src/test/java/g2301_2400/s2351_first_letter_to_appear_twice/SolutionTest.java

@@ -15,4 +15,9 @@ void repeatedCharacter() {
     void repeatedCharacter2() {
         assertThat(new Solution().repeatedCharacter("abcdd"), equalTo('d'));
     }
+
+    @Test
+    void repeatedCharacter3() {
+        assertThat(new Solution().repeatedCharacter("abcd"), equalTo('0'));
+    }
 }