华为机试练习150817第二题：求后序序列

import java.util.Scanner;

/**
 * Created by cq on 2015/8/17 22:22.
 * 根据前序序列和中序序列，求后序序列，否则输出No
 * 这里没有对输入参数的合法性进行验证，因为合法性由机试系统保证
 * 测试例：
 8
 1 2 4 7 3 5 6 8
 4 7 2 1 5 3 8 6
 8
 1 2 4 7 3 5 6 8
 4 1 2 7 5 3 8 6
 8
 1 2 4 5 3 6 7 8
 4 5 2 1 6 3 9 7
 * 结果：
 7 4 2 5 8 6 3 1
 No
 5 4 2 6 9 7 3 1
 */
public class Main {
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        try {
            while (in.hasNextInt()){
                int lenOfTree = in.nextInt();

                int[] preorder = new int[lenOfTree], inorder = new int[lenOfTree];
                for (int i=0; i<lenOfTree; i++){
                    preorder[i] = in.nextInt();
                }
                for (int i=0; i<lenOfTree; i++){
                    inorder[i] = in.nextInt();
                }

                String result = isBTree(preorder, 0, preorder.length - 1, inorder, 0, inorder.length - 1);
                if (result.indexOf("s") != -1){
                    result = "No";
                }
                System.out.println(result);
            }
        }catch (Exception e){}
        finally {
            in.close();
        }

    }

    public static String isBTree(int[] preorder, int pBegin, int pEnd, int[] inorder, int iBegin, int iEnd){
        if (iBegin == iEnd){
            return inorder[iBegin]+" ";
        }
        else if (iBegin > iEnd){
            return "";
        }
        int root = preorder[pBegin], indexOfRoot = indexOf(inorder, iBegin, iEnd, root);
        if (indexOfRoot == -1){
            return "s";
        }
        int leftLen = indexOfRoot-iBegin;
        return  isBTree(preorder, pBegin+1, pBegin+leftLen, inorder, iBegin, indexOfRoot-1)
                + isBTree(preorder, pBegin+leftLen+1, pEnd, inorder, indexOfRoot+1, iEnd) +root+" ";
    }
    public static int indexOf(int[] arr, int froIndex, int endIndex, int target){
        for (int i=froIndex; i<=endIndex; i++){
            if (arr[i] == target){
                return i;
            }
        }
        return -1;
    }
}