Problem

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 s, int numRows);

Code

class Solution {
public:
    string convert(string s, int numRows) {
        string result;
        if(numRows <= 1 || s.length() == 0)
            return s;
        if(numRows == 2){
            for (int i = 0; i < s.length(); i = i + 2) {
                result.append(1,s[i]);
            }
            for (int j = 1; j < s.length(); j = j + 2) {
                result.append(1,s[j]);
            }
            return result;
        }
        int len = s.length();
        int max = 2 * numRows - 2;//定义最大间隔
        int change = max;//初始化change，在循环中change是可能被改变的
        for (int i = 0; i < numRows; i++)
        {
            if(i == 0)
            {//处理第一行的情况
                for (int j = 0; j < len; j = j + max) {
                    result.append(1,s[j]);
                }
            }
            else if (i == numRows - 1)//处理最后一行的情况
            {
                for (int j = numRows - 1; j < len; j = j + max) {
                    result.append(1,s[j]);
                }
            }

            else{//处理其他行的情况
                change = change - 2;
                for (int j = i; j < len;j = j + max) {
                    result.append(1,s[j]);
                    if(j + change < len)
                        result.append(1,s[j + change]);
                }
            }
        }
        return result;
    }
};