add leetcodea: offer-34-36-54

Author: CodeWater404

Algorithm/src/offer/_34ThePathOfBinaryTreeNeutralityIsACertainValue.java

@@ -0,0 +1,52 @@
+package offer;
+
+import java.util.LinkedList;
+import java.util.List;
+
+/**
+ * @author ： CodeWater
+ * @create ：2022-07-07-17:45
+ * @Function Description ：34. 二叉树中和为某一值的路径
+ */
+public class _34ThePathOfBinaryTreeNeutralityIsACertainValue {
+    /**
+     * Definition for a binary tree node.
+     * public class TreeNode {
+     *     int val;
+     *     TreeNode left;
+     *     TreeNode right;
+     *     TreeNode() {}
+     *     TreeNode(int val) { this.val = val; }
+     *     TreeNode(int val, TreeNode left, TreeNode right) {
+     *         this.val = val;
+     *         this.left = left;
+     *         this.right = right;
+     *     }
+     * }
+     */
+    class Solution {
+        // 总方案
+        public LinkedList<List<Integer>> res = new LinkedList<>();
+        // 记录当前搜索的一种方案
+        public LinkedList<Integer> path = new LinkedList<>();
+
+        public List<List<Integer>> pathSum(TreeNode root, int target) {
+            dfs(root , target);
+            return res;
+
+        }
+
+        // 先序遍历  
+        public void dfs(TreeNode root , int target ){
+            if( root == null ) return ;
+            path.add( root.val );
+            target -=root.val;
+            if( target == 0 && root.left == null && root.right == null ){
+                res.add( new LinkedList( path ) );
+            }
+            dfs( root.left , target );
+            dfs( root.right , target );
+            path.removeLast();
+        }
+    }
+}

Algorithm/src/offer/_36TheBinarySearchTreeAndTwoWayLinkedList.java

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+package offer;
+
+/**
+ * @author ： CodeWater
+ * @create ：2022-07-07-18:24
+ * @Function Description ：36.二叉搜索树与双向链表
+ */
+
+// Definition for a Node.
+class Node1 {
+    public int val;
+    public Node1 left;
+    public Node1 right;
+
+    public Node1() {}
+
+    public Node1(int _val) {
+        val = _val;
+    }
+
+    public Node1(int _val,Node1 _left,Node1 _right) {
+        val = _val;
+        left = _left;
+        right = _right;
+    }
+};
+
+
+public class _36TheBinarySearchTreeAndTwoWayLinkedList {
+    
+    class Solution {
+        // pre上一个结点，left变成指向上一个结点的指针，right是下一个
+        public Node1 pre , head;
+        public Node1 treeToDoublyList(Node1 root) {
+            if( root == null ) return null;
+            dfs(root);
+            head.left = pre;
+            pre.right = head;
+            return head;
+        }
+
+        // 中序
+        public void dfs( Node1 cur ){
+            if( cur == null ) return ;
+            dfs( cur.left );
+            // 前一个结点不空，right指针指向当前
+            if( pre != null ) pre.right = cur;
+                // 前一个结点空，找到头结点或者
+            else head = cur;
+            // 当前结点left指向上一个
+            cur.left = pre;
+            // pre移到当前结点
+            pre = cur;
+            dfs( cur.right );
+        }
+    }
+}

Algorithm/src/offer/_54TheKNodeOfTheBinarySearchTree.java

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+package offer;
+
+/**
+ * @author ： CodeWater
+ * @create ：2022-07-07-18:41
+ * @Function Description ：54.二叉搜索树的第k大结点
+ */
+public class _54TheKNodeOfTheBinarySearchTree {
+    /**
+     * Definition for a binary tree node.
+     * public class TreeNode {
+     *     int val;
+     *     TreeNode left;
+     *     TreeNode right;
+     *     TreeNode(int x) { val = x; }
+     * }
+     */
+    class Solution {
+        public int res  , k ;
+        public int kthLargest(TreeNode root, int k) {
+            this.k = k;
+            dfs( root );
+            return res;
+
+        }
+
+        // 中序遍历的倒序，右根左
+        public void dfs( TreeNode root ){
+            if( root == null ) return ;
+            dfs( root.right );
+            if( k == 0 ) return ;
+            if( --k == 0 ) res = root.val;
+
+            dfs( root.left );
+
+        }
+    }
+}