leetcode——6——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".

输出之字形结构

class Solution {
public:
string convert(string s, int nRows){

    if(nRows == 1) return s;

    string res[nRows];

    int i = 0, j, gap = nRows-2;

    while(i < s.size()){

        for(j = 0; i < s.size() && j < nRows; ++j) res[j] += s[i++];

        for(j = gap; i < s.size() && j > 0; --j) res[j] += s[i++];

    }

    string str = "";

    for(i = 0; i < nRows; ++i)

        str += res[i];

    return str;

} 
};