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[leetcode]Construct Binary Tree from Inorder and Postorder Traversal - java

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根据后序集合找到根,再根据根,在中序集合中找到索引号,采用递归的构建子树的方法

/**

 * Definition for binary tree

 * public class TreeNode {

 *     int val;

 *     TreeNode left;

 *     TreeNode right;

 *     TreeNode(int x) { val = x; }

 * }

 */

public class Solution {

    public TreeNode buildTree(int[] inorder, int[] postorder) {

        return gT(inorder, 0, inorder.length-1, postorder, 0, postorder.length-1);

    }



    private TreeNode gT(int[] inorder, int inStart, int inEnd, int[] postorder, int pStart, int pEnd){

        if(inorder==null || postorder==null || inorder.length==0 || postorder.length==0 || inStart>inEnd || pStart>pEnd){

            return null;

        }

        int childRootVal = postorder[pEnd];

        TreeNode childRoot = new TreeNode(childRootVal);

        int childRootInOrderIndex = -1;

        for(int i=inStart; i<=inEnd; i++){

            if(inorder[i]==childRootVal){

                childRootInOrderIndex=i;

                break;

            }

        }

        if(childRootInOrderIndex==-1){

            return null;

        }

        int duration = childRootInOrderIndex-inStart;

        childRoot.left=gT(inorder, inStart, childRootInOrderIndex - 1, postorder, pStart, pStart + duration - 1);

        childRoot.right=gT(inorder, childRootInOrderIndex+1,inEnd, postorder, pStart+duration, pEnd-1);

        return childRoot;

    }

}

 

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