[LEET-3438] add 3438

Author: fishercoder1534

paginated_contents/algorithms/4th_thousand/README.md

@@ -5,6 +5,7 @@
 | 3477 | [Fruits Into Baskets II](https://leetcode.com/problems/fruits-into-baskets-ii/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3477.java) |                                                                               | Easy       |
 | 3471 | [Find the Largest Almost Missing Integer](https://leetcode.com/problems/find-the-largest-almost-missing-integer/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3471.java) |                                                                               | Easy       |
 | 3450 | [Maximum Students on a Single Bench](https://leetcode.com/problems/maximum-students-on-a-single-bench/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3450.java) |                                                                               | Easy       |
+| 3438 | [Find Valid Pair of Adjacent Digits in String](https://leetcode.com/problems/find-valid-pair-of-adjacent-digits-in-string/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3438.java) |                                                                               | Easy       |
 | 3402 | [Minimum Operations to Make Columns Strictly Increasing](https://leetcode.com/problems/minimum-operations-to-make-columns-strictly-increasing/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3402.java) |                                                                               | Easy       |
 | 3396 | [Minimum Number of Operations to Make Elements in Array Distinct](https://leetcode.com/problems/minimum-number-of-operations-to-make-elements-in-array-distinct/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3396.java) |                                                                               | Easy       |
 | 3392 | [Count Subarrays of Length Three With a Condition](https://leetcode.com/problems/count-subarrays-of-length-three-with-a-condition/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3392.java) |                                                                               | Easy       |

src/main/java/com/fishercoder/solutions/fourththousand/_3438.java

@@ -0,0 +1,24 @@
+package com.fishercoder.solutions.fourththousand;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class _3438 {
+    public static class Solution1 {
+        public String findValidPair(String s) {
+            Map<Integer, Integer> map = new HashMap<>();
+            for (char c : s.toCharArray()) {
+                int val = Character.getNumericValue(c);
+                map.put(val, map.getOrDefault(val, 0) + 1);
+            }
+            for (int i = 0; i < s.length() - 1; i++) {
+                int val = Character.getNumericValue(s.charAt(i));
+                int nextVal = Character.getNumericValue(s.charAt(i + 1));
+                if (val != nextVal && val == map.get(val) && nextVal == map.get(nextVal)) {
+                    return val + "" + nextVal + "";
+                }
+            }
+            return "";
+        }
+    }
+}