根据二叉树的前序和中序获得后序，后序和中序获得前序

根据二叉树的前序和中序获得后序，后序和中序获得前序的实现。可以用递归，呵呵！

下面是我写的测试程序：

package algorithm; public class BTree { private static StringBuilder postOrderReverse = new StringBuilder();// 储存后序的一个逆行 private static StringBuilder preOrder = new StringBuilder();// 储存前序 /** * 根据先序和中序，获得后序 * * @param preOrder * @param inOrder */ public static void getPostOrder(String preOrder, String inOrder) { if (preOrder.length() == 1 && inOrder.length() == 1) { postOrderReverse.append(preOrder); return; } char root = preOrder.charAt(0); int rootIndex = -1; String left_InOrder = null; String left_preOrder = null; String right_Inorder = null; String right_preOrder = null; postOrderReverse.append(root);// 将跟节点放入 rootIndex = inOrder.indexOf(root); left_InOrder = inOrder.substring(0, rootIndex);// 左子树 的中序 right_Inorder = inOrder.substring(rootIndex + 1);// 右子树的中序 preOrder = preOrder.substring(1); int size = left_InOrder.length(); int index = -1; for (int i = 0; i < size; ++i) { int tmp = preOrder.indexOf(left_InOrder.charAt(i)); if (index < tmp) index = tmp; } left_preOrder = preOrder.substring(0, index + 1);// 左子树前序 right_preOrder = preOrder.substring(index + 1);// 右子树前序 if (right_preOrder != null && !right_Inorder.equals("")) getPostOrder(right_preOrder, right_Inorder); if (left_preOrder != null && !left_preOrder.equals("")) getPostOrder(left_preOrder, left_InOrder); } /** * 根据后序和中序 ，获得先序 * * @param postOrder * @param inOrder */ public static void getPreOrder(String postOrder, String inOrder) { if (postOrder.length() == 1 && inOrder.length() == 1) { preOrder.append(postOrder); return; } String root = postOrder.substring(postOrder.length() - 1); int rootIndex = -1; String left_InOrder = null; String left_postOrder = null; String right_Inorder = null; String right_postOrder = null; preOrder.append(root); rootIndex = inOrder.indexOf(root); left_InOrder = inOrder.substring(0, rootIndex);// 左子树中序 right_Inorder = inOrder.substring(rootIndex + 1);// 右子树中序 int index = -1; int size = left_InOrder.length(); for (int i = 0; i < size; ++i) { int tmp = postOrder.indexOf(left_InOrder.charAt(i)); if (tmp > index) index = tmp; } left_postOrder = postOrder.substring(0, index + 1);// 左 子树后序 right_postOrder = postOrder .substring(index + 1, postOrder.length() - 1);// 右子树后序 if (left_InOrder != null && !left_InOrder.equals("") && left_postOrder != null && !left_postOrder.equals("")) getPreOrder(left_postOrder, left_InOrder); if (right_Inorder != null && !right_Inorder.equals("") && right_postOrder != null && !right_postOrder.equals("")) getPreOrder(right_postOrder, right_Inorder); } public static void main(String[] args) { getPostOrder("BCAD", "CBAD"); System.out.println(postOrderReverse.reverse()); getPreOrder("ACBFGED", "ABCDEFG"); System.out.println(preOrder); } }