leetcode-6-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 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

总之就是，画图找规律。。。

这里边界条件别忘记判断（其实很简单，就是判断下标是否超出了s.size()即可

class Solution { public: string convert(string s, int numRows) { if(numRows==1) return s; string ans=""; int round_size=2*(numRows-1); for(int i=0;i<numRows;i++) for(int j=0;j<=s.size()/round_size;j++){ //the first number int first = j*round_size + i; if(first < s.size()) //边界条件的写法！！！ ans += s[first]; int second = first + round_size - i*2; if(i!=0 && i!=numRows-1 && second < s.size()) ans += s[second]; } return ans; } };