LeetCode 006 ZigZag Conversion

题目描述：ZigZag Conversion

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 text, int nRows);

convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".

分析：

对于每一层垂直元素的坐标 ( i, j ) = ( j + 1) ∗ n + i；对于每两层垂直元素之间的插入元素（斜对角元素）， ( i, j ) = ( j + 1) ∗ n − i。

代码如下：

class Solution {
public:
    string convert(string s, int nRows) {
        
        if(nRows <= 1 || s.size() <= 1) return s;
        string result;
        
        for(int i = 0; i < nRows; i++){
            for(int j = 0, index = i; index < s.size(); j++, index = (2 * nRows - 2) * j + i){
                result.append(1, s[index]);
                if(i == 0 || i == nRows - 1) continue;
                if(index + (nRows - i - 1) * 2 < s.size())
                    result.append(1, s[index + (nRows - i - 1) * 2]);
            }
        }
        
        return result;
        
    }
};