6.ZigZag Conversion

题目描述

将字符串 "PAYPALISHIRING" 以Z字形排列成给定的行数：

P   A   H   N
A P L S I I G
Y   I   R

之后从左往右，逐行读取字符："PAHNAPLSIIGYIR"

实现一个将字符串进行指定行数变换的函数:

string convert(string s, int numRows);

示例 1:

输入: s = "PAYPALISHIRING", numRows = 3
输出: "PAHNAPLSIIGYIR"

示例 2:

输入: s = "PAYPALISHIRING", numRows = 4
输出: "PINALSIGYAHRPI"

解释:

P     I    N
A   L S  I G
Y A   H R
P     I

JS解法

/**
 * @param {string} s
 * @param {number} numRows
 * @return {string}
 */
var convert = function(s, numRows) {
    if (numRows <= 1) {
        return s;
    }
    let result = [];
    let index = 0, step = 1;
    for (let i = 0; i < s.length; i++) {
        if (result[i] === undefined) { //如果没有这个步骤，会在string中加入'undefined'
            result[i] = '';
        }
        result[index] += s[i];
        if (index === 0) {
            step = 1;
        } else if (index === numRows - 1) {
            step = -1;
        }
        index += step;
    }
    return result.join('');
};