字符串：PAYPALISHIRING，4行展示的”Z”字形图案为

输出为：PINALSIGYAHRPI

char* convert(char* s, int numRows) {
	if (numRows == 1) 
		return s;

	int i = 0, j = 0, span, span1 = 0, span2 = 0, k = 0, sPos = 0, flag = 1;
	int len = strlen(s);
	char* res = (char*)malloc(sizeof(char) * (len + 1));
	res[0] = '\0';

	for (i = numRows; i > 0; i--) {
		span1=2* (i - 1);//间距分两部分，设置标志位计算下一位置，间距为0时，因为已经访问过，直接跳过
		span2=2* (numRows - 1) - span1;
		flag = 1;
		
		j = sPos;
		sPos++;
		while (j < len) {
			if (flag == 1) {
				span = span1;
				flag = -1;
			}
			else {
				span = span2;
				flag = 1;
			}
			if (span == 0) {
				continue;
			}

			res[k] = s[j];
			k++;
			res[k] = '\0';
			j += span;
		}
	}
	return res;
}