116. 填充每个节点的下一个右侧节点指针（算法200题-69）

var connect = function(root) {
    if(!root) return root
    const list = [[root]],
          resList = []
    const dfs = (root, list, count = 1) => {
        if(!root || (!root.left && !root.right)) return
        const current = list[count] = list[count] ? list[count] : []
        if(root.left) {
            current.push(root.left)
        }
        if(root.right) {
            current.push(root.right)
        }
        dfs(root.left, list, count + 1)
        dfs(root.right, list, count + 1)
    } 
    dfs(root, list)
    for(let i = 0; i < list.length; i++) {
        for(let j = 0; j < list[i].length; j++) {
            list[i][j].next = list[i][j + 1] ? list[i][j + 1] : null
        }
    }
    return root
};