617. Merge Two Binary Trees

[Tcdian]

617. Merge Two Binary Trees

给定两个二叉树，想象当你将它们中的一个覆盖到另一个上时，两个二叉树的一些节点便会重叠。

你需要将他们合并为一个新的二叉树。合并的规则是如果两个节点重叠，那么将他们的值相加作为节点合并后的新值，否则不为 NULL 的节点将直接作为新二叉树的节点。

Example

Input: 
    Tree 1                     Tree 2                  
          1                         2                             
         / \                       / \                            
        3   2                     1   3                        
       /                           \   \                      
      5                             4   7                  
Output: 
Merged tree:
         3
        / \
       4   5
      / \   \ 
     5   4   7

Note

• 合并必须从两个树的根节点开始。

[Tcdian]

Solution

• JavaScript Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} t1
 * @param {TreeNode} t2
 * @return {TreeNode}
 */
var mergeTrees = function(t1, t2) {
    if (t1 === null) {
        return t2;
    }
    if (t2 === null) {
        return t1;
    }
    return new TreeNode(t1.val + t2.val, mergeTrees(t1.left, t2.left), mergeTrees(t1.right, t2.right));
};

• TypeScript Solution

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

function mergeTrees(t1: TreeNode | null, t2: TreeNode | null): TreeNode | null {
    if (t1 === null) {
        return t2;
    }
    if (t2 === null) {
        return t1;
    }
    return new TreeNode(t1.val + t2.val, mergeTrees(t1.left, t2.left), mergeTrees(t1.right, t2.right));
};