# 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('')
};

```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://mm.ricky.moe/algorithm/algorithm-and-data-structure/leetcode/6.zzi-xing-bian-huan.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.