72 - 中序遍历和后序遍历树构造二叉树

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本文介绍了一种根据二叉树的后序遍历和中序遍历结果来重建该二叉树的方法。通过递归地确定根节点，并划分左子树和右子树的遍历序列，最终构建出完整的二叉树结构。

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2017.9.8

这个和

前序遍历和中序遍历树构造二叉树

是差不多的

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
 
 
public class Solution {
    /**
     *@param inorder : A list of integers that inorder traversal of a tree
     *@param postorder : A list of integers that postorder traversal of a tree
     *@return : Root of a tree
     */
   	  public TreeNode buildTree(int[] inorder, int[] postorder) {
	        // write your code here
		  if(inorder == null || postorder == null || inorder.length != postorder.length || inorder.length == 0){
			  return null;
		  }
		  TreeNode root = new TreeNode(postorder[postorder.length-1]);
		  for(int i = 0; i < inorder.length; i++){
			  if(inorder[i] == root.val){
				  int []inLeft = Arrays.copyOfRange(inorder, 0, i);
				  int []inRight = Arrays.copyOfRange(inorder, i+1, inorder.length);
				  int []postRight = Arrays.copyOfRange(postorder, inLeft.length, postorder.length-1);
				  int []postLeft = Arrays.copyOfRange(postorder, 0, inLeft.length);
				  root.left = buildTree(inLeft,postLeft);
				  root.right = buildTree(inRight,postRight);
			  }
		  }
		  return root;
	    }
}