> For the complete documentation index, see [llms.txt](https://mm.ricky.moe/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mm.ricky.moe/algorithm/algorithm-and-data-structure/leetcode/6.zzi-xing-bian-huan.md).

# 6. Z字形变换

## 题目

将一个给定字符串根据给定的行数，以从上往下、从左到右进行 Z 字形排列。

比如输入字符串为 `"LEETCODEISHIRING"` 行数为 3 时，排列如下：

```
L   C   I   R
E T O E S I I G
E   D   H   N
```

之后，你的输出需要从左往右逐行读取，产生出一个新的字符串，比如：`"LCIRETOESIIGEDHN"`。

请你实现这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 = "LEETCODEISHIRING", numRows = 3
输出: "LCIRETOESIIGEDHN"
```

**示例 2:**

```
输入: s = "LEETCODEISHIRING", numRows = 4
输出: "LDREOEIIECIHNTSG"
解释:

L     D     R
E   O E   I I
E C   I H   N
T     S     G
```

## 思路

按顺序遍历字符串的`s`为单个字符为c ，设置flag =1

1. res\[i] += c
2. 更新i += flag
3. 到达Ｚ的转折点为　flag = -flag

```javascript
/**
 * @param {string} s
 * @param {number} numRows
 * @return {string}
 */
var convert = function(s, numRows) {
  if( numRows === 1) return s

  let res = new Array(numRows).fill('')
  let flag = -1
  let i = 0

  for (const c of s) {
    if(i === 0 || i === numRows -1 )flag = -flag
    res[i] += c

    i += flag
  }
  
  return res.join('')
};

```


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