ZigZag Conversion leetcode

he 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" .

就是纯粹的找规律。

发现所有行的重复周期都是 2 * nRows - 2

对于首行和末行之间的行，还会额外重复一次，重复的这一次距离本周期起始字符的距离是 2 * nRows - 2 - 2 * i

class Solution {
public:
    string convert(string s, int nRows) {
        if(nRows<2)
            return s;
        string res;
        for(int i=0;i<nRows;i++) {
            for(int j=i;j<s.size();j += 2*(nRows-1)) {
                res.push_back(s[j]);
                if(i>0 && i<nRows-1) {
                    if(j+2*(nRows-1-i) <s.size()) {
                        res.push_back(s[j+2*(nRows-1-i)]);
                    }
                }
            }
        }
        return res;
    }
};