Review: BFS Problems

// Blog link: https://code.dennyzhang.com/maximum-level-sum-of-a-binary-tree
// Basic Ideas: bfs
//
// Complexity: Time O(n), Space O(n)
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func maxLevelSum(root *TreeNode) int {
    level, maxSum, res := 1, -1<<31, 0

    queue := []*TreeNode{root}
    for len(queue) != 0 {
        l := []*TreeNode{}
        sum := 0
        for _, node := range queue {
            sum += node.Val
            if node.Left != nil {
                l = append(l, node.Left)
            }
            if node.Right != nil {
                l = append(l, node.Right)
            }
        }
        if sum > maxSum {
            maxSum, res = sum, level
        }
        queue = l
        level++
    }
    return res
}