SOURCE

class Queue {
    arr = []

    push (item) {
        this.arr.push(item)
    }
    pop() {
        return this.arr.shift()
    }
    getArr() {
        return this.arr
    }
    size () {
        return this.arr.length
    }

    isEmpty () {
        return this.arr.length === 0
    }
}

class Node {
    data = ''
    left = null
    right = null
}

function fib(n = 1, arr = []) {
    if (n === 1 || n === 2) return 1

    if(arr[n]) return arr[n]

    arr[n] = fib( n - 1, arr) + fib(n - 2, arr)

    return arr[n]
}
// console.log(fib(1000))
let res = []
function backtrack(str = '', arr = '') {
    if (arr.length === str.length) {
        res.push(arr)
        return 
    }
   
    for(let i = 0; i < str.length; i++) {
        if (arr.indexOf(str[i]) !== -1) {
            continue
        }
        arr += str[i]
        backtrack(str, arr)
        arr = arr.substr(0, arr.length - 1)
    }
}
// backtrack('12345678')

let resNQ = []
const isValid = (board, row, col) => {
    let m = board.length
    let n = board[0].length
    let flag = true
    // row
    for(let i = 0; i < n; i++) {

    }
    return flag

}
function solveNQueens (board, row = 0) {
    if (row === board.length) {
        resNQ.push(board)
        return 
    }

    let n = board[row].length
    for(let col = 0; col < n; col++) {
        if (!isValid(board, row, col)) {
            continue
        }
        // console.log(row, col)
        board[row][col]  = 'Q'
        solveNQueens(board, row + 1)
        board[row][col]  = '.'
    }
}
let board = []
for(let i = 0; i < 4; i++) {
    let res = []
    for(let j = 0; j < 4; j++) {
        res.push('.')
    }
    board.push(res)
}

let q = new Queue() 
q.push(1)
q.push(2)

console.log(q.getArr())
console.log(q.pop())


let treeArr= [3, 9, 20, null, null, 15, 7]
const createNode = (i, data)=> {
    if (i >= data.length) return null
    let node = new Node()
    node.data = data[i]
    node.left = createNode(i + 1, data)
    node.right = createNode(i + 2, data)
    return node
}
console.log(createNode(0,treeArr))