leetcode-N 字形变换

/**
 * @param {string} s
 * @param {number} numRows
 * @return {string}
 */
var convert = function(s, numRows) {
    if(numRows == 0 || numRows == 1){
        return s
    }
    //设定一个返回结果的数组
    let res = new Array(numRows).fill("")
    res
    // 规定一个count
    let count = 0 
    //方向
    let a = 1
    for(let i = 0; i < s.length; i++){
        res[count] += s[i]
        count = count + a
        if(count == 0){
            a = 1
        }
        if(count == numRows -1){
            a = -1
        }
    }
    
    return res.join("")
};