19.1.20 [LeetCode 6]ZigZag Conversion

Medium

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 s, int numRows);

Example 1:

Input: s = "PAYPALISHIRING", numRows = 3
Output: "PAHNAPLSIIGYIR"

Example 2:

Input: s = "PAYPALISHIRING", numRows = 4
Output: "PINALSIGYAHRPI"
Explanation:

P     I    N
A   L S  I G
Y A   H R
P     I

class Solution {
public:
    string convert(string s, int numRows) {
        int group = numRows + numRows - 2;
        if (group <=1)return s;
        int i, size = s.length();
        string ans = "";
        for (int i = 0; i < size; i += group)
            ans+=s[i];
        for (int j = 1; j < numRows-1; j++) {
            for (i = 0; i < size; i += group) {
                if(i+j<size)
                    ans+=s[i+j];
                if(i+group-j<size)
                    ans+=s[i + group - j];
            }
        }
        for (int i = numRows - 1; i < size; i += group)
            ans+=s[i];
        return ans;
    }
};

简单的模拟，坑点在于有类似 numRows=1 的情况