【树】C005_二叉树的坡度（递归）

Given a binary tree, return the tilt of the whole tree.

The tilt of a tree node is defined as the absolute difference between the sum of all left subtree node values and the sum of all right subtree node values. Null node has tilt 0.

The tilt of the whole tree is defined as the sum of all nodes’ tilt.

Input: 
         1
       /   \
      2     3
Output: 1
Explanation: 
Tilt of node 2 : 0
Tilt of node 3 : 0
Tilt of node 1 : |2-3| = 1
Tilt of binary tree : 0 + 0 + 1 = 1

二、题解

方法一：递归

核心：求出该结点的左子树结点和右子树结点和的差值。

int tilt= 0;
public int findTilt(TreeNode root) {
  sup(root);
  return tilt;
}

private int sup(TreeNode root) {
  if (root == null)
    return 0;

  int L_Sum=  sup(root.left);
  int R_Sum = sup(root.right);
  tilt += Math.abs(L_Sum - R_Sum );
  
  int curr_sum = L_Sum + R_Sum + root.val;

  return curr_sum;
}

复杂度分析

• 时间复杂度： $O(N)$，
• 空间复杂度： $O(N / log(N))$，