重建二叉树

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 package cn.feng; class Node { Node left = null; Node right = null; char value; } public class BinaryTreeBuilder { /** * 根据前序遍历和中序遍历重建二叉树子树 * @param preOrder 前序遍历数组 * @param start 子树起始位置 * @param inOrder 中序遍历数组 * @param end 中序遍历结束位置 * @param length 子树节点数字 * @return 子树的根节点 */ public static Node buildTree(char[] preOrder, int start, char[] inOrder, int end, int length) { //参数验证 if (preOrder == null || preOrder.length == 0 || inOrder == null || inOrder.length == 0 || length <= 0) { return null; } //建立子树根节点 char value = preOrder[start]; Node root = new Node(); root.value = value; //递归终止条件：子树只有一个节点 if (length == 1) return root; //分拆子树的左子树和右子树 int i = 0; while (i < length) { if (value == inOrder[end - i]) { break; } i++; } //建立子树的左子树 root.left = buildTree(preOrder, start + 1, inOrder, end - i - 1, length - 1 - i); //建立子树的右子树 root.right = buildTree(preOrder, start + length - i, inOrder, end, i ); return root; } public static void main(String[] args) { char[] preOrder = new char[] {'a', 'b', 'd', 'c', 'e', 'f'}; char[] inOrder = new char[] {'d', 'b', 'a', 'e', 'c', 'f'}; Node root = buildTree(preOrder, 0, inOrder, inOrder.length - 1, inOrder.length); } }