leetcode——106.从中序和后序遍历序列构造二叉树

还可以，自己做得出来。

public TreeNode buildTree(int[] inorder, int[] postorder) {
        //用一个map来存储中序
        int n = inorder.length;
        if(n == 0){
            return null;
        }else if(n == 1){
            return new TreeNode(inorder[0]);
        }
        Map<Integer,Integer> map = new HashMap<>();
        for(int i = 0;i<n;i++){
            map.put(inorder[i],i);
        }
        TreeNode root = new TreeNode(postorder[n-1]);
        //构建左子树
        int i = map.get(postorder[n-1]);   //找到根节点在中序遍历中的下标值
        root.left = buildTree(inorder,postorder,0,i-1,0,i-1,map);
        //构建右子树
        root.right = buildTree(inorder,postorder,i+1,n-1,i,n-2,map);
        return root;
    }

    private TreeNode buildTree(int[] inorder, int[] postorder, int in_start, int in_end, int post_start, int post_end,Map<Integer,Integer> map) {
        if(post_end < post_start){
            return null;
        }
        TreeNode node = new TreeNode(postorder[post_end]);
        int i = map.get(postorder[post_end]);
        node.left = buildTree(inorder, postorder, in_start, i, post_start, post_start+i-in_start-1, map);
        node.right = buildTree(inorder, postorder, i+1, in_end, post_start+i-in_start, post_end-1, map);
        return node;
    }

——2020.7.1