[LeetCode]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，用一个idx 从0-->(nRows-1)---->0 来回往返，将对应的字符加入到strs[idx]的字符串中，最后汇总所有的字符串，

注意，当nRows == 1的情况需要特使处理，否则idx-- 后，idx变成-1，会越界crash

class Solution {
    public:
        string convert(string s, int nRows) {
            if(nRows == 1)
                return s;
                
            vector<string> strs;
            strs.resize(nRows);
            string result;

            int idx = 0;
            bool upOrDown = false;// false--down, true--up

            for(size_t i = 0; i< s.size(); i++)
            {   
                strs[idx] += s[i];
                if(upOrDown == false)
                {   
                    if(idx == (nRows-1))
                    {   
                        upOrDown = true;
                        idx--;
                    }   
                    else
                    {   
                        idx++;
                    }   
                }   
                else
                {   
                    if(idx == 0)
                    {   
                        upOrDown = false;
                        idx++;
                    }   
                    else
                    {   
                        idx--;
                    }
                }
            }
            for(size_t i = 0; i< strs.size(); i++)
            {
                result += strs[i];
            }

            return result;
        }
};