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[Golang][Leetcode][BinaryTree]刷題系列-515-Find Largest Value in Each Tree Row


515. Find Largest Value in Each Tree Row


Level : Medium

原題連結 : Click

題目 :

Given the root of a binary tree, return an array of the largest value in each row of the tree (0-indexed).


Example :

Note

Example 1:

Input: root = [1,3,2,5,3,null,9] Output: [1,3,9]

Example 2:

Input: root = [1,2,3] Output: [1,3]

Example 3:

Input: root = [1] Output: [1]

Example 4:

Input: root = [1,null,2] Output: [1,2]

Example 5:

Input: root = [] Output: []


解題思路 :

  • 這題是level order traversal的變化題,一樣可以用queue來解決,可以參考 leetcode102題解
  • 這類題目解法都差不多,需要要每個level 最大的value取出來就ok了!

Queue解法

  • time complexity: O(n) , space complexity: O(n)

Runtime: 4 ms, faster than 98.39% of Go online submissions for Find Largest Value in Each Tree Row.


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/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func largestValues(root *TreeNode) []int {
    
    var res []int
    
    if root == nil {
        return res
    }
    
    var queue []*TreeNode
    
    queue = append(queue,root)
    
    
    for len(queue) != 0 {
        
        length := len(queue)
        
        max := queue[0].Val
        
        for i := 0; i < length; i++ {
            
            node := queue[0]
            
            if node.Val > max {
                max = node.Val
            }
            
            if node.Left != nil {
                queue = append(queue, node.Left)
            }
            
            if node.Right != nil {
                queue = append(queue, node.Right)
            }
            
            queue = queue[1:]
        }
        
        res = append(res, max)
        
    }
    
    return res
}

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