# ZigZag Conversion

### 描述​

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   NA P L S I I GY   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".

### 分析​

n=4:

P     I     NA   L S   I GY A   H RP     I

n=5:

P       HA     S IY   I   RP L     I  GA       N

### 代码​

// ZigZag Conversion// 时间复杂度O(n)，空间复杂度O(1)public class Solution {    public String convert(String s, int numRows) {        if (numRows <= 1 || s.length() <= 1) return s;        StringBuilder result = new StringBuilder();        for (int i = 0; i < numRows; i++) {            for (int j = 0, index = i; index < s.length();                 j++, index = (2 * numRows - 2) * j + i) {                result.append(s.charAt(index));  // 垂直元素                if (i == 0 || i == numRows - 1) continue;   // 斜对角元素                if (index + (numRows - i - 1) * 2 < s.length())                    result.append(s.charAt(index + (numRows - i - 1) * 2));            }        }        return result.toString();    }}