public class Tree<AnyType extends Comparable<? super AnyType>> { private static class BinaryNode<AnyType> {BinaryNode(AnyType theElement) { this(theElement, null, null); } BinaryNode(AnyType theElement, BinaryNode<AnyType> lt, BinaryNode<AnyType> rt) { element = theElement; left = lt; right = rt; } AnyType element; BinaryNode<AnyType> left; BinaryNode<AnyType> right; }private BinaryNode<AnyType> root; public void insert(AnyType x) { root = insert(x, root); } private BinaryNode<AnyType> insert(AnyType x, BinaryNode<AnyType> t) { if(t == null) { return new BinaryNode<>(x, null, null); } int compareResult = x.compareTo(t.element); if(compareResult < 0) { t.left = insert(x, t.left); } else if(compareResult > 0) { t.right = insert(x, t.right); } else { ; } return t; } /** * 前序遍歷 */ public void preOrder(BinaryNode<AnyType> Node) { if (Node != null) { System.out.print(Node.element + " ");preOrder(Node.left); preOrder(Node.right); } } /** * 中序遍歷*/ public void midOrder(BinaryNode<AnyType> Node) { if (Node != null) { midOrder(Node.left); System.out.print(Node.element + " "); midOrder(Node.right); } } /** * 後序遍歷 */ public void posOrder(BinaryNode<AnyType> Node) { if (Node != null) {posOrder(Node.left); posOrder(Node.right); System.out.print(Node.element + " "); } } /* * 層序遍歷 * 遞歸*/ public void levelOrder(BinaryNode<AnyType> Node) { if (Node == null) { return; } int depth = depth(Node); for (int i = 1; i <= depth; i++) { levelOrder(Node, i); } } private void levelOrder(BinaryNode<AnyType> Node, int level) { if (Node == null || level < 1) { return; } if (level == 1) { System.out.print(Node.element + " "); return; } // 左子樹levelOrder(Node.left, level - 1); // 右子樹levelOrder(Node.right, level - 1); } public int depth(BinaryNode<AnyType> Node) { if (Node == null) {return 0; } int l = depth(Node.left); int r = depth(Node.right); if (l > r) { return l + 1; } else { return r + 1; } } public static void main( String[] args ) { int[] input = {4, 2, 6, 1, 3, 5, 7, 8, 10}; Tree<Integer> tree = new Tree<>(); for(int i = 0; i < input.length; i++) { tree.insert(input[i]); } System.out.print( "前序遍歷 ：" ); tree.preOrder(tree.root); System.out.print( "\n中序遍歷 ：" ); tree.midOrder(tree.root); System.out.print( "\n後序遍歷 ：" ); tree.posOrder(tree.root); System.out.print("\n遞歸層序遍歷："); tree.levelOrder(tree.root); } }

Java實現二叉樹的前序、中序、後序、層序遍歷（遞歸方法）