6. ZigZag Conversion (Medium)
https://leetcode.com/problems/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
Solutions
class Solution {
// Zigzag is a pattern that repeats every numRows * 2 - 2 chars. To find out the
// pattern, put the elements into a matrix.
// The the row size is numRows, the columns size
// should be (s.length() / (numRows * 2 - 2) + numRows - 1) * (numRows-1), where
// s.length() / (numRows * 2 - 2) + 1 is the number of pattern groups.
// Literally, adding 1 or not depends on specific situation. But to make it easier, I always advise
// to add; numRows - 1 is the number of chars in each ziazag pattern.
public String convert(String s, int numRows) {
String ans = "";
if (s == null || s.length() == 0) {
return ans;
}
if (numRows == 1) {
return s;
}
int len = s.length();
int groupSize = 2 * numRows - 2;
for (int i = 0; i < numRows; i++) {
for (int j = i; j < len; j += groupSize) {
ans += s.charAt(j);
// Make sure char index is within the boundary.
if (i % (numRows - 1) != 0 && j + groupSize - 2 * i < len) {
ans += s.charAt(j + groupSize - 2 * i);
}
}
}
return ans;
}
}