添加 InOrderTraversal.java

InOrderTraversal.java

@@ -0,0 +1,78 @@
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Stack;
+
+public class InOrderTraversal {
+
+    public static void main(String[] args) {
+        TreeNode root = new TreeNode(1);
+
+        root.left = new TreeNode(2);
+        root.right = new TreeNode(3);
+
+        root.left.left = new TreeNode(4);
+        root.left.right = new TreeNode(5);
+
+        List<Integer> result = inOrderTraversal(root);
+        System.out.println(result); // 输出: [4, 2, 5, 1, 3]
+
+        List<Integer> result2 = inOrderTraversalNonRecursive(root);
+        System.out.println(result2); // 输出: [4, 2, 5, 1, 3]
+    }
+
+    // 中序遍历二叉树
+    public static class TreeNode {
+        int val;
+        TreeNode left;
+        TreeNode right;
+
+        TreeNode(int x) {
+            val = x;
+        }
+    }
+
+    // 递归中序遍历方法
+    public static List<Integer> inOrderTraversal(TreeNode root) {
+        List<Integer> result = new ArrayList<>();
+        forEach(root, result);
+        return result;
+    }
+
+    public static void forEach(TreeNode node, List<Integer> result) {
+        if (node != null) {
+            // 左子树
+            forEach(node.left, result);
+            // 处理节点数据
+            result.add(node.val);
+            // 右子树
+            forEach(node.right, result);
+        }
+    }
+
+    // 非递归中序遍历方法
+    public static List<Integer> inOrderTraversalNonRecursive(TreeNode root) {
+        if (root == null) {
+            return null;
+        }
+
+        Stack<TreeNode> stack = new Stack<>();
+        TreeNode current = root;
+        List<Integer> result = new ArrayList<>();
+
+        while (current != null || !stack.isEmpty()) {
+            // 将当前节点的所有左子节点压入栈中
+            while (current != null) {
+                stack.push(current);
+                current = current.left;
+            }
+            // 弹出栈顶并访问
+            current = stack.pop();
+            result.add(current.val);
+            // 转向右子树
+            current = current.right;
+        }
+
+        return result;
+    }
+
+}