leetcode | ZigZag Conversion

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   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“.

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将字符串按之字形排列，然后按行输出。
本题的关键点在于找出每一行两个元素之间的间隔，通过画图找规律。

如上图所示，4行，第一行和最后一行两个元素之间的下标之差是k = 2*numRows-2; 其他的i行是，第一次间隔2*i,第二次则是k-2*i,然后交替进行，直到索引超出数组。

class Solution {public:    string convert(string s, int numRows) {    int size = s.size();    if (size == 0 || numRows <= 1)        return s;    string result;    int k = 2 * (numRows - 1); // 最大间隔    int t = 0; //标记奇偶    for (int i = 0; i < numRows; i++) {        t = 0;        for (int j = i; j < size;) {            result.push_back(s[j]);            if (i == 0 || i == numRows - 1)                j += k;            else if (t%2 == 0) // 第偶数次                j += (k - 2 * i);            else if (t%2 == 1) // 第奇数次                j += (2 * i);            t++;        }    }    return result;}};