【leetcode】107.二叉树的层序遍历 II

leetcode-107.png

层次遍历，只不过是从最底层开始放入数组中

BFS

var levelOrderBottom = function (root) {
    if (!root) return []
    let res = []
    let queue = []
    queue.push(root)
    while (queue.length) {
        let size = queue.length
        let level = []
        for (let i = 0; i < size; ++i) {
            let node = queue.shift()
            level.push(node.val)
            if (node.left) queue.push(node.left)
            if (node.right) queue.push(node.right)
        }
        res.unshift(level)
    }
    return res
};