(二叉搜索树10.1.2)POJ 1577 Falling Leaves(根据删除叶子节点的顺序输出计算一颗二叉树的前序遍历序列)

package com.njupt.acm;import java.util.Scanner;public class POJ_1577 {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);int levels = 0;String line;String[] leaves = new String[26];while(scanner.hasNext()){line = scanner.nextLine().trim();if(line.equals("*")){System.out.println(preorder(leaves, levels));leaves = new String[26];levels = 0;}else if(line.equals("$")){System.out.println(preorder(leaves, levels));break;}else{leaves[levels++] = line;}}}public static String preorder(String[] leaves,int levels){//将根据leaves中的行序列计算前序遍历序列while(levels > 0 && leaves[levels-1].length() == 0){//从leaves[]标的最后一项开始找,找到第一个非空项..levels--;}if(levels == 0){return "";}levels--;char root = leaves[levels].charAt(0);//leaves表尾存储子根String[] left = new String[levels];String[] right = new String[levels];int i;for(i = 0 ; i < levels ; ++i){int past = 0;while(past < leaves[i].length() && leaves[i].charAt(past) < root){//找到左右子树的分界点past++;}left[i] = leaves[i].substring(0,past);right[i] = leaves[i].substring(past);}return root + preorder(left, levels) + preorder(right, levels);}}