Cousins in Binary Tree II
<p>Given the <code>root</code> of a binary tree, replace the value of each node in the tree with the <strong>sum of all its cousins&#39; values</strong>.</p>

<p>Two nodes of a binary tree are <strong>cousins</strong> if they have the same depth with different parents.</p>

<p>Return <em>the </em><code>root</code><em> of the modified tree</em>.</p>

<p><strong>Note</strong> that the depth of a node is the number of edges in the path from the root node to it.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/2600-2699/2641.Cousins%20in%20Binary%20Tree%20II/images/example11.png" style="width: 571px; height: 151px;" />
<pre>
<strong>Input:</strong> root = [5,4,9,1,10,null,7]
<strong>Output:</strong> [0,0,0,7,7,null,11]
<strong>Explanation:</strong> The diagram above shows the initial binary tree and the binary tree after changing the value of each node.
- Node with value 5 does not have any cousins so its sum is 0.
- Node with value 4 does not have any cousins so its sum is 0.
- Node with value 9 does not have any cousins so its sum is 0.
- Node with value 1 has a cousin with value 7 so its sum is 7.
- Node with value 10 has a cousin with value 7 so its sum is 7.
- Node with value 7 has cousins with values 1 and 10 so its sum is 11.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/2600-2699/2641.Cousins%20in%20Binary%20Tree%20II/images/diagram33.png" style="width: 481px; height: 91px;" />
<pre>
<strong>Input:</strong> root = [3,1,2]
<strong>Output:</strong> [0,0,0]
<strong>Explanation:</strong> The diagram above shows the initial binary tree and the binary tree after changing the value of each node.
- Node with value 3 does not have any cousins so its sum is 0.
- Node with value 1 does not have any cousins so its sum is 0.
- Node with value 2 does not have any cousins so its sum is 0.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree is in the range <code>[1, 10<sup>5</sup>]</code>.</li>
	<li><code>1 &lt;= Node.val &lt;= 10<sup>4</sup></code></li>
</ul>
Tree; Depth-First Search; Breadth-First Search; Hash Table; Binary Tree
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func replaceValueInTree(root *TreeNode) *TreeNode {
	s := []int{}
	var dfs1 func(*TreeNode, int)
	dfs1 = func(root *TreeNode, depth int) {
		if root == nil {
			return
		}
		if len(s) <= depth {
			s = append(s, 0)
		}
		s[depth] += root.Val
		dfs1(root.Left, depth+1)
		dfs1(root.Right, depth+1)
	}
	var dfs2 func(*TreeNode, int)
	dfs2 = func(root *TreeNode, depth int) {
		l, r := 0, 0
		if root.Left != nil {
			l = root.Left.Val
		}
		if root.Right != nil {
			r = root.Right.Val
		}
		sub := l + r
		depth++
		if root.Left != nil {
			root.Left.Val = s[depth] - sub
			dfs2(root.Left, depth)
		}
		if root.Right != nil {
			root.Right.Val = s[depth] - sub
			dfs2(root.Right, depth)
		}
	}
	dfs1(root, 0)
	root.Val = 0
	dfs2(root, 0)
	return root
}