add 55.TreeDepth

src/_55/TreeDepth.java

@@ -0,0 +1,65 @@
+package _55;
+
+import java.util.LinkedList;
+import java.util.Queue;
+
+import structure.TreeNode;
+
+// 二叉树的深度
+// 输入一棵二叉树的根结点，求该树的深度。从根结点到叶结点依次经过的
+// 结点（含根、叶结点）形成树的一条路径，最长路径的长度为树的深度。
+public class TreeDepth {
+  public static int treeDepthRecursively(TreeNode root) {
+    if (root == null) {
+      return 0;
+    }
+    int left = treeDepthRecursively(root.left);
+    int right = treeDepthRecursively(root.right);
+    return (left > right) ? left + 1 : right + 1;
+  }
+
+  public static int treeDepthIteratively(TreeNode root) {
+    if (root == null) {
+      return 0;
+    }
+
+    Queue<TreeNode> queue = new LinkedList<>();
+    queue.offer(root);
+    int depth = 0;
+
+    while (!queue.isEmpty()) {
+      int size = queue.size();
+      for (int i = 0; i < size; i++) {
+        TreeNode node = queue.poll();
+        if (node.left != null) {
+          queue.offer(node.left);
+        }
+        if (node.right != null) {
+          queue.offer(node.right);
+        }
+      }
+      depth++;
+    }
+
+    return depth;
+  }
+
+  public static void main(String[] args) {
+    //            1
+    //         /     \
+    //        2        3
+    //       /\         \
+    //      4  5         6
+    //        /
+    //       7
+    TreeNode root = new TreeNode(1);
+    root.left = new TreeNode(2);
+    root.left.left = new TreeNode(4);
+    root.left.right = new TreeNode(5);
+    root.left.right.left = new TreeNode(7);
+    root.right = new TreeNode(3);
+    root.right.right = new TreeNode(6);
+    System.out.println(treeDepthRecursively(root)); // 4
+    System.out.println(treeDepthIteratively(root));
+  }
+}