ZigZag Conversion

Desicription

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)

1
2
3
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:

1
string convert(string text, int nRows);

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

Solution

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
class Solution {
public:
    string convert(string s, int numRows) {
        if(numRows <= 1 || s.size() <= numRows)
            return s;
        string res;
        int s_size = s.size();
        for(int i = 0; i < numRows; i++){
            if(i == 0 || i == numRows-1){
                int index = i;
                while(index < s_size){
                    res += s[index];
                    index += (numRows - 1) * 2;
                }
            }
            else{
                int index = i;
                while(index < s_size){
                    res += s[index];
                    if(index + (numRows-i-1) * 2 < s_size)
                        res += s[index + (numRows-i-1) * 2];
                    index += (numRows - 1) * 2;
                }
            }
        }
        return res;
    }
};