队列方法解leetcode之404-二叉树的左叶子之和

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/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func sumOfLeftLeaves(root *TreeNode) int {
    // 直接层序遍历，将叶子结点的值相加即可
    var total int
    if root == nil {
        return total
    }
    queue := []*TreeNode{root}
    for len(queue) > 0 {
        curr := queue[0]
        queue = queue[1:]
        if curr.Left != nil {
            queue = append(queue, curr.Left)
            // 这一条件保证是叶子结点
            if curr.Left.Left == nil && curr.Left.Right == nil {
                total += curr.Left.Val
            }
        }
        if curr.Right != nil {
            queue = append(queue, curr.Right)
        }
    }
    return total
}