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; } }