重建二叉树

已知二叉树的前序和中序遍历序列，以此重建二叉树。

重建二叉树，必须知道前序和中序序列，其他组合都不行。

public class RebuildTree {

class Node{

int nodeValue;

        Nodeleft;

        Noderight;

        Node(){}

Node(int nodeValue, Node left, Node right){

this.nodeValue = nodeValue;

            this.left = left;

            this.right = right;

        }

Node(int nodeValue) {

this.nodeValue = nodeValue;

            this.left =null;

            this.right =null;

        }

}

public NoderebuildTree(int[] preOrder, int[] inOrder)throws Exception {

if(preOrder ==null || preOrder.length ==0 || inOrder ==null || inOrder.length ==0){

throw new Exception("Invalid input!");

        }

return constructTree(preOrder, 0, preOrder.length -1, inOrder, 0, inOrder.length -1);

    }

private NodeconstructTree(int[] preOrder, int startIndex4PreOrder, int endIndex4PreOrder, int[] inOrder, int startIndex4InOrder, int endIndex4InOrder)throws Exception{

if(startIndex4PreOrder == endIndex4PreOrder){

if(startIndex4InOrder == endIndex4InOrder){

return new Node(preOrder[startIndex4PreOrder]);

            }

throw new Exception("InValid input!");

        }

//取preOrder的第一个数做root

        int rootValue = preOrder[startIndex4PreOrder];

        Node rootNode =new Node(rootValue);

        //遍历inOrder找到rootValue

        int rootIndex = findIndexOfNumber(inOrder, rootValue);

        if(rootIndex == -1){

throw new Exception("InValid input!");

        }

int leftTreeSize = rootIndex - startIndex4InOrder;

        int rightTreeSize = endIndex4InOrder - rootIndex;

        //如果leftTreeSize > 0，则存在左子树，创建左子树

        if(leftTreeSize >0) {

rootNode.left = constructTree(preOrder, startIndex4PreOrder +1, startIndex4PreOrder + leftTreeSize, inOrder, startIndex4InOrder, startIndex4InOrder + leftTreeSize -1);

        }

//如果rightTreeSize > 0，则存在右子树，创建右子树

        if(rightTreeSize >0){

rootNode.right = constructTree(preOrder, startIndex4PreOrder + leftTreeSize +1, endIndex4PreOrder, inOrder, rootIndex +1, endIndex4InOrder);

        }

return rootNode;

    }

private int findIndexOfNumber(int[] seq, int num) {

for(int i =0; i < seq.length; i++) {

if(seq[i] == num){

return i;

            }

}

return -1;

    }

public ListpreOrderSeq(Node rootNode, List result){

//输出root节点

        if(rootNode ==null){

return result;

        }

result.add(rootNode.nodeValue);

        //输出左子树

        if(rootNode.left !=null) {

preOrderSeq(rootNode.left, result);

        }

//输出右子树

        if(rootNode.right !=null) {

preOrderSeq(rootNode.right, result);

        }

return result;

    }

public static void main(String[] args) {

try {

int[] preOrder = {10,6,3,8,15,13,17};

            int[] inOrder = {3,6,8,10,13,15,17};

            List result =new ArrayList<>();

            RebuildTree rebuildTree =new RebuildTree();

            result = rebuildTree.preOrderSeq(rebuildTree.rebuildTree(preOrder, inOrder), result);

            for(Integer item : result){

System.out.println(" " + item +" ");

            }

}catch (Exception e){}

}

}