重建二叉树

package algorithm;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);}}