6. ZigZag Conversion

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本文介绍了一种将字符串以Z形模式排列并按行读取的方法。通过提供的代码示例，展示了如何实现这一转换过程，即将输入字符串PAYPALISHIRING按照指定行数进行Z形排列，并最终按行顺序读取输出。

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".

/*n=numRows
Δ=2n-2    1                           2n-1                         4n-3
Δ=        2                     2n-2  2n                    4n-4   4n-2
Δ=        3               2n-3        2n+1              4n-5       .
Δ=        .           .               .               .            .
Δ=        .       n+2                 .           3n               .
Δ=        n-1 n+1                     3n-3    3n-1                 5n-5
Δ=2n-2    n                           3n-2                         5n-4
*/

题目乍一看不知道啥意思。

class Solution {
public:
    string convert(string s, int numRows) {
        string result = "";
        if(numRows == 1)
        return s;
        int step1,step2;
        int len = s.size();
        for(int i = 0; i < numRows; ++i)
        {
            step1 = (numRows-i-1)*2;
            step2 = 2*i;
            int pos = i;
            if(pos < len)
            result += s.at(pos);
            while(1)
            {
                pos += step1;
                if(pos >= len)
                break;
                if(step1)                   //不能省，
                result += s.at(pos);
                pos += step2;
                if(pos >= len)              //是>=   而不是>
                break;
                if(step2)
                result += s.at(pos);
            }
            
        }
        return result;
        
    }
};