重构C函数以查找O(n）中二进制树的直径到JavaScript

Refactoring C function to find diameter of Binary Tree in O(n) to JavaScript

本文关键字：二进制 JavaScript 函数 查找 重构      更新时间：2023-09-26

我很难理解/重写这里给出的用于查找二叉树直径的"优化"C函数。我不明白它是如何记录高度的。我知道它使用了第二个参数height来实现这一点，但在代码中我甚至没有看到使用了height参数。我很难理解C语言中的函数，我主要用JavaScript编写。我能够重写页面上的所有其他函数，尽管没有问题。

/*The second parameter is to store the height of tree.
   Initially, we need to pass a pointer to a location with value
   as 0. So, function should be used as follows:
   int height = 0;
   struct node *root = SomeFunctionToMakeTree();
   int diameter = diameterOpt(root, &height); */
int diameterOpt(struct node *root, int* height)
{
  /* lh --> Height of left subtree
      rh --> Height of right subtree */
  int lh = 0, rh = 0;
  /* ldiameter  --> diameter of left subtree
      rdiameter  --> Diameter of right subtree */
  int ldiameter = 0, rdiameter = 0;
  if(root == NULL)
  {
    *height = 0;
     return 0; /* diameter is also 0 */
  }
  /* Get the heights of left and right subtrees in lh and rh
    And store the returned values in ldiameter and ldiameter */
  ldiameter = diameterOpt(root->left, &lh);
  rdiameter = diameterOpt(root->right, &rh);
  /* Height of current node is max of heights of left and
     right subtrees plus 1*/
  *height = max(lh, rh) + 1;
  return max(lh + rh + 1, max(ldiameter, rdiameter));
}

通过引用传递的近似等价物（在您提供的示例中也有注释）将是属性为的对象

var heightHolder = { height:0};
var diam = diameterOpt(root, heightHolder);
console.log(heightHolder.height);
function diameterOpt(root, heightHolder){
   if (!root)  {
      heightHolder.height = 0; 
      return 0;
   }
   var refLh = {height:0};
   var refRh = {height:0};
   var ldiameter = diameterOpt(root.left, refLh); 
   ....
   heightHolder.height = Math.max(refLh.height, refRh.height) + 1;
   return ...
}

通常情况下，你不会走JavaScript支持以更自然的方式返回多个值这样疯狂的路线：

 function diameterOpt(root){
    if (!root){
       return {height:0, diameter:0};
    }
    var leftResult = diameterOpt(root.left);
    var rightResult = diameterOpt(root.right);
    return {
       height:  Math.max(leftResult.height,rightResult.height) + 1;
       diameter: 
           Math.max(leftResult.height+rightResult.height + 1,
                    Math.max(leftResult.diameter, rightResult.diameter))
       }  
}
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