二叉树遍历和重建

输入2行整数，第1行表示二叉树的中序遍历，第2行表示二叉树的前序遍历，以空格分割。
请由该二叉树生成一个新的二叉树，它满足其树中的每个节点将包含原始树中的左子树和右子树的和。

public static void main1(String[] args) {  
// int[] inArr = new int[]{6,5,3 ,7, -2, 6, 6, 9, 3};  
// int[] preArr = new int[]{6 ,7, 5, 6, 3, -2, 9, 6, 3};  
  
// int[] inArr = new int[]{6,5};  
// int[] preArr = new int[]{6 ,5};  
  
  
int[] preArr = new int[]{10, -2, 8, -4, 6, 7, 5};  
int[] inArr = new int[]{8, -2, -4, 10, 7, 6, 5};  
  
final Tree tree = buildTree(inArr, preArr);  
  
inPrint(tree);  
System.out.println();  
prePrint(tree);  
  
}  
  
public static Tree buildTree(int[] inArr, int[] preArr) {  
//校验数据  
if (inArr.length == 0 || inArr.length != preArr.length) {  
return null;  
}  
//前序遍历的第一个元素就是 root  
Tree root = new Tree();  
if (inArr.length == 1) {  
root.value = 0;  
return root;  
//递归的逻辑就是先找到root  
// 然后root.left=左子树的root  
// root.right=右子树的root  
//问题变成寻找左右子树  
// 然后递归。  
  
}  
  
//如果只有两个值判断是左元素还是右元素  
if (inArr.length == 2) {  
Tree tree = new Tree(0);  
for (int i = 0; i < 2; i++) {  
if (inArr[0] == preArr[0]) {  
root.right = tree;  
root.value = preArr[1];  
} else {  
root.left = tree;  
root.value = preArr[0];  
}  
}  
  
return root;  
}  
  
//在中序遍历中找到root元素，左边的就是左子树，右边的就是右子树  
for (int i = 1; i < inArr.length; i++) {  
if (inArr[i] == preArr[0]) {  
//可能是根节点  
int[] inLeftArr = Arrays.copyOfRange(inArr, 0, i);  
int[] preLeftArr = Arrays.copyOfRange(preArr, 1, i + 1);  
int[] inRightArr = Arrays.copyOfRange(inArr, i + 1, inArr.length);  
int[] preRightArr = Arrays.copyOfRange(preArr, i + 1, preArr.length);  
root.value = sum(inLeftArr) + sum(inRightArr);  
//判断左右子树是否相等  
if (arrEquals(inLeftArr, preLeftArr) && arrEquals(inRightArr, preRightArr)) {  
root.left = buildTree(inLeftArr, preLeftArr);  
root.right = buildTree(inRightArr, preRightArr);  
break;  
}  
}  
}  
  
  
return root;  
}  
  
public static int sum(int[] arr) {  
int sum = 0;  
for (int i = 0; i < arr.length; i++) {  
sum += arr[i];  
}  
return sum;  
}  
  
public static boolean arrEquals(int[] a1, int[] a2) {  
int[] arr1 = Arrays.copyOf(a1, a1.length);  
int[] arr2 = Arrays.copyOf(a2, a2.length);  
Arrays.sort(arr1);  
Arrays.sort(arr2);  
return Arrays.equals(arr1, arr2);  
}  
  
public static void main(String[] args) {  
Tree root = new Tree(6);  
Tree t7 = new Tree(7);  
root.left = t7;  
Tree t9 = new Tree(9);  
root.right = t9;  
  
Tree t_2 = new Tree(-2);  
t7.right = t_2;  
  
Tree t6 = new Tree(6);  
t9.left = t6;  
  
Tree t5 = new Tree(5);  
t7.left = t5;  
Tree t3 = new Tree(3);  
t9.right = t3;  
  
// Tree t6_ = new Tree(6);  
// t5.left = t6_;  
//  
// t5.right = t3;  
  
  
prePrint(root);  
System.out.println();  
inPrint(root);  
System.out.println();  
afterPrint(root);  
  
}  
  
public static void prePrint(Tree root) {  
if (root == null) {  
return;  
}  
System.out.print(root.value + " ");  
prePrint(root.left);  
prePrint(root.right);  
}  
  
public static void inPrint(Tree root) {  
if (root == null) {  
return;  
}  
inPrint(root.left);  
System.out.print(root.value + " ");  
inPrint(root.right);  
}  
  
public static void afterPrint(Tree root) {  
if (root == null) {  
return;  
}  
afterPrint(root.left);  
afterPrint(root.right);  
System.out.print(root.value + " ");  
}  
  
static class Tree {  
int value;  
Tree left;  
Tree right;  
  
public Tree() {  
}  
  
public Tree(int value) {  
this.value = value;  
}  
}