[算法练习]ZigZag Conversion

题目说明：

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".

程序代码：

#include <gtest/gtest.h>
using namespace std;

string convert(string s, int numRows)
{
    if (s.empty() || (numRows < 2))
    {
        return s;
    }

    string result;
    int length = s.length();
    char* data = new char[length*numRows];
    memset(data,0,length * numRows);

    int delta = 0;
    int offset = 0;
    int flag = 1;

    for (int i= 0; i<length; ++i)
    {
        data[offset + delta * length] = s[i];        
        if ( (delta+flag) >= numRows)
        {
            flag = -1;
        }
        else if ((delta+flag) < 0)
        {
            flag = 1;
        }
        delta += flag;

        if (flag == -1)
        {
            offset ++;
        }
    }

    for (int i=0; i<numRows; ++i)
    {
        for (int j=0; j < length; ++j)
        {
            if (data[j+i*length])
                result += data[j+i*length];
        }
    }

    delete data;

    return result;
}

TEST(Pratices, tZigZagConversion)
{
    // ''=> ''
    // ABCDEFG 3 => A   E  => AEBDFCG
    //              B D F 
    //              C   G

    ASSERT_EQ(convert("",1),"");
    ASSERT_EQ(convert("ABCDEFG",1),"ABCDEFG");
}