# 2022-06-24

## [515. Find Largest Value in Each Tree Row](https://leetcode.com/problems/find-largest-value-in-each-tree-row/)

### Description

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

**Example 1:**

![](https://img.content.cc/a/2022/06/24/19-48-58-253-ebcc9691b584d98fbb7c867c84a0f536-37871d.png)

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

**Example 2:**

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

**Constraints:**

* The number of nodes in the tree will be in the range `[0, 10^4]`.
* `-2^31 <= Node.val <= 2^31 - 1`

### Solution

#### Approach #0: BFS

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

func max(a, b int) int {
    if a > b {
        return a
    }
    return b
}
```

#### Approach #1: DFS

```go
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func largestValues(root *TreeNode) (ans []int) {
    if root == nil {
        return
    }
    var dfs func(*TreeNode, int)
    dfs = func(node *TreeNode, depth int) {
        if node == nil {
            return
        }
        if len(ans) <= depth {
            ans = append(ans, node.Val)
        } else {
            ans[depth] = max(ans[depth], node.Val)
        }
        dfs(node.Left, depth+1)
        dfs(node.Right, depth+1)
    }
    dfs(root, 0)
    return
}

func max(a, b int) int {
    if a > b {
        return a
    }
    return b
}
```


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