[leetcode][string] ZigZag Conversion

题目：

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   NA P L S I I GY   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".

class Solution {public:string convert(string s, int numRows) {if (s.size() <= 1 || numRows <= 1) return s;string res;int n = s.size();for (int i = 0; i < numRows; ++i){if (i == 0 || i == numRows - 1){int step = 2 * (numRows - 1);for (int j = i; j < n; j += step){res.push_back(s[j]);}}else{bool isEven = true;int step;for (int j = i; j < n; j += step){res.push_back(s[j]);step = isEven ? 2 * (numRows - i - 1) : 2 * i;isEven ^= 1;//取反}}}return res;}};