ZigZag Conversion - LeetCode JavaScript

题目

The string " PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

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

And then read line by line: "PAHNAPLSIIGYIR"
Write the code that will take a string and make this conversion given a number of rows:
string convert(string text, int nRows);
convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".

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题目解释

假设咱们输入的就是上面的字符串,在numRows取不一样值的时候,你们看我用Excel作的简易的图:

看完图应该就明白了这个题目究竟是什么意思,这个题的难点在于找规律,只要找到了规律,解决这个题并不难.
规律以下:

• 第一行或者最后一行,元素之间的间隔(distance)为
  2 * nRows - 2;
• 中间部分间隔分别是:
  distace - 2i, 2 i, distance - 2i, 2i...

  依照上面规律,代码以下

/**
 * @param {string} s
 * @param {number} numRows
 * @return {string}
 */
var convert = function(s, numRows) {
    if (numRows <= 1)
        return s;
    let res = '';
    let len = s.length;
    let dis = numRows*2 - 2;
    
    /* first row */
    for (let i = 0; i < len; i+=dis) {
        res += s.charAt(i);
    }
    
    /* middle */
    for (let i = 1; i < numRows-1; i++) {
        let tempDis = 2*i;
        for (let j = i; j < len; j += tempDis) {
            res += s.charAt(j);
            tempDis = dis - tempDis;
        }
    }
    
    /* last row */
    for (let i = numRows-1; i< len; i += dis) {
        res += s.charAt(i);
    }
    return res;
};