java实现——006重建二叉树

public class T006 {
public static void main(String[] args){
int pre[] = {1,2,4,7,3,5,6,8};
int in[] = {4,7,2,1,5,3,8,6};
preorderTraversalRec(construct(pre,in,8));

}
public static void preorderTraversalRec(TreeNode root) {
if (root == null) {
return;
}
System.out.print(root.val + " ");
preorderTraversalRec(root.left);
preorderTraversalRec(root.right);
}
public static TreeNode construct(int[] pre,int[] in,int length){
if(pre == null ||in == null||length<=0)
return null;
return constructCore(pre,in,0,length-1,0,length-1);

}
public static TreeNode constructCore(int[] pre,int[] in,int startPre,int endPre,int startIn,int endIn){
int rootValue = pre[startPre];
TreeNode root = new TreeNode(rootValue);
root.left = null;
root.right = null;
if(startPre == endPre){
if(startIn == endIn&&startPre==startIn){
System.out.println("root");
return root;
}
}
int rootIn = startIn;
while(rootIn<=endIn&&in[rootIn]!=rootValue){
++ rootIn;
}
if(rootIn == endIn&&in[rootIn]!=rootValue){
System.out.println("Invalid input2");
}
int leftLength = rootIn - startIn;
int leftPreEnd = startPre + leftLength;
if(leftLength>0){
root.left = constructCore(pre,in,startPre+1,leftPreEnd,startIn,rootIn-1);
}
if(leftLength<endPre-startPre){
root.right = constructCore(pre,in,leftPreEnd+1,endPre,rootIn+1,endIn);
}
return root;

}
private static class TreeNode {
int val;
TreeNode left;
TreeNode right;

public TreeNode(int val) {
this.val = val;
}
}
}