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".

思路：直接模拟就行。一开始想了各种下标的复杂转换，真是没有必要。

这题还学到了两个知识点：

1. 想申请一个数组的话，比如string eg[56];这样写的话所申请的数组规模必须预先给定，对于不能确定的数组，申请要动态申请，比如 string *eg = new string[num];

2. string的append和+运算的区别：append是直接在原字符串的末尾添加，+运算是生成一个新的string来存储运算结果。

class Solution {
public:
    string convert(string s, int numRows) {
        if (numRows == 1) return s;
        string *res = new string[numRows];
        int step = 1, row = 0;
        for (char c : s)
        {
            if (row == 0)
                step = 1;
            else if (row == numRows - 1)
                step = -1;
            res[row] += c;
            row += step;
        }
        string ans;
        for (int i = 0; i < numRows; i++)
            ans.append(res[i]);
        return ans;
    }
};