add 2689

Author: fishercoder1534

Diff for: paginated_contents/algorithms/3rd_thousand/README.md

@@ -25,6 +25,7 @@
 | 2706 | [Buy Two Chocolates](https://leetcode.com/problems/buy-two-chocolates/)                                                                                                                     | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2706.java)                                       |                                 | Easy                           |
 | 2697 | [Lexicographically Smallest Palindrome](https://leetcode.com/problems/lexicographically-smallest-palindrome/)                                                            | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2697.java)                                       |                                 | Easy                           |
 | 2696 | [Minimum String Length After Removing Substrings](https://leetcode.com/problems/minimum-string-length-after-removing-substrings/)                                                           | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2696.java)                                       |                                 | Easy                           |
+| 2689 | [Extract Kth Character From The Rope Tree](https://leetcode.com/problems/extract-kth-character-from-the-rope-tree/)                                                                                     | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2689.java)                                       |                                 | Easy                           |
 | 2682 | [Find the Losers of the Circular Game](https://leetcode.com/problems/find-the-losers-of-the-circular-game/)                                                                                     | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2682.java)                                       |                                 | Easy                           |
 | 2673 | [Make Costs of Paths Equal in a Binary Tree](https://leetcode.com/problems/make-costs-of-paths-equal-in-a-binary-tree/)                                                                                     | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2673.java)                                       |                                 | Medium                         |Tree, DFS, Greedy
 | 2678 | [Number of Senior Citizens](https://leetcode.com/problems/number-of-senior-citizens/)                                                                                      | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2678.java)                                       |                                 | Easy                           |

Diff for: src/main/java/com/fishercoder/solutions/thirdthousand/_2689.java

@@ -0,0 +1,51 @@
+package com.fishercoder.solutions.thirdthousand;
+
+public class _2689 {
+    //      Definition for a rope tree node.
+    public static class RopeTreeNode {
+        public int len;
+        public String val;
+        public RopeTreeNode left;
+        public RopeTreeNode right;
+
+        public RopeTreeNode() {
+        }
+
+        public RopeTreeNode(String val) {
+            this.len = 0;
+            this.val = val;
+        }
+
+        public RopeTreeNode(int len) {
+            this.len = len;
+            this.val = "";
+        }
+
+        public RopeTreeNode(int len, RopeTreeNode left, RopeTreeNode right) {
+            this.len = len;
+            this.val = "";
+            this.left = left;
+            this.right = right;
+        }
+    }
+
+    public static class Solution1 {
+        /**
+         * My completely original solution.
+         */
+        public char getKthCharacter(RopeTreeNode root, int k) {
+            StringBuilder sb = new StringBuilder();
+            postOrderToConcatenate(root, k, sb);
+            return sb.charAt(k - 1);
+        }
+
+        private void postOrderToConcatenate(RopeTreeNode root, int k, StringBuilder sb) {
+            if (sb.length() >= k || root == null) {
+                return;
+            }
+            postOrderToConcatenate(root.left, k, sb);
+            postOrderToConcatenate(root.right, k, sb);
+            sb.append(root.val);
+        }
+    }
+}

Diff for: src/test/java/com/fishercoder/thirdthousand/_2689Test.java

@@ -0,0 +1,57 @@
+package com.fishercoder.thirdthousand;
+
+import com.fishercoder.solutions.thirdthousand._2689;
+import com.fishercoder.solutions.thirdthousand._2976;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class _2689Test {
+    private static _2689.Solution1 solution1;
+
+    @BeforeEach
+    public void setup() {
+        solution1 = new _2689.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        _2689.RopeTreeNode root = new _2689.RopeTreeNode();
+        root.len = 12;
+        root.val = "";
+
+        _2689.RopeTreeNode rootLeft = new _2689.RopeTreeNode();
+        rootLeft.len = 6;
+        rootLeft.val = "";
+        root.left = rootLeft;
+
+        _2689.RopeTreeNode rootLeftLeft = new _2689.RopeTreeNode();
+        rootLeftLeft.len = 3;
+        rootLeftLeft.val = "abc";
+        rootLeft.left = rootLeftLeft;
+
+        _2689.RopeTreeNode rootLeftRight = new _2689.RopeTreeNode();
+        rootLeftRight.len = 3;
+        rootLeftRight.val = "efg";
+        rootLeft.right = rootLeftRight;
+
+        _2689.RopeTreeNode rootRight = new _2689.RopeTreeNode();
+        rootRight.len = 6;
+        rootRight.val = "";
+        root.right = rootRight;
+
+        _2689.RopeTreeNode rootRightLeft = new _2689.RopeTreeNode();
+        rootRightLeft.len = 3;
+        rootRightLeft.val = "hij";
+        rootRight.left = rootRightLeft;
+
+        _2689.RopeTreeNode rootRightRight = new _2689.RopeTreeNode();
+        rootRightRight.len = 3;
+        rootRightRight.val = "klm";
+        rootRight.right = rootRightRight;
+
+
+        assertEquals('c', solution1.getKthCharacter(root, 3));
+    }
+}