[leetcode]Construct Binary Tree from Inorder and Postorder Traversal

这题难就难在分段index是什么
要想仔细！！

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

public class Solution { HashMap<Integer, Integer> rootIndex = new HashMap<Integer, Integer>(); public TreeNode buildTree(int[] inorder, int[] postorder) { for (int i = 0; i < inorder.length; i++){ rootIndex.put(inorder[i], i); } return buildTree_rec(0, inorder.length-1, 0, postorder.length-1, postorder); } private TreeNode buildTree_rec(int instart, int inend, int poststart, int postend, int[]postorder){ if (poststart > postend) return null; int root_i = rootIndex.get(postorder[postend]); TreeNode root = new TreeNode(postorder[postend]); root.left = buildTree_rec(instart, root_i-1, poststart, poststart+(root_i-instart)-1,postorder); root.right = buildTree_rec(root_i+1, inend, poststart+(root_i-instart), postend-1, postorder); return root; } }