有中序遍历和后序遍历构建二叉树

 

 

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func buildTree(inorder []int, postorder []int) *TreeNode {
    return build(inorder,0,len(inorder)-1,postorder,0,len(postorder)-1)
}

func build(inorder []int,s1,e1 int,postorder []int,s2,e2 int)*TreeNode{
    if s1>e1{
        return nil
    }
    //根节点的值肯定是后序遍历的最后一个节点
    rootVal:=postorder[e2]
    //在中序遍历结果里查找根节点的索引
    inIdx:=s1
    for i:=s1;i<e1;i++{
        if rootVal==inorder[i]{
            inIdx=i
            break
        }
    }
    //构造根节点
    root:=&TreeNode{}
    root.Val=rootVal
    //递归构造左右子树
    leftSize:=inIdx-s1
    root.Left=build(inorder,s1,inIdx-1,postorder,s2,s2+leftSize-1)
    root.Right=build(inorder,inIdx+1,e1,postorder,s2+leftSize,e2-1)
    return root
}