6.zig-zag-conversion.java

/*
 * @lc app=leetcode id=6 lang=java
 *
 * [6] ZigZag Conversion
 *
 * https://leetcode.com/problems/zigzag-conversion/description/
 *
 * algorithms
 * Medium (30.72%)
 * Likes:    1101
 * Dislikes: 3404
 * Total Accepted:    338.3K
 * Total Submissions: 1M
 * Testcase Example:  '"PAYPALISHIRING"\n3'
 *
 * 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
 *
 */
class Solution {
  public String convert(String s, int numRows) {
    if (numRows == 1) {
      return s;
    }

    StringBuilder sb = new StringBuilder();
    int len = s.length();
    int cycle = 2 * numRows - 2;

    for (int i = 0; i < numRows; i++) {
      for (int j = 0; j + i < len; j += cycle) {
        sb.append(s.charAt(j + i));
        if ((i != 0) && (i != numRows - 1) && (j + cycle - i < len)) {
          sb.append(s.charAt(j + cycle - i));
        }
      }
    }

    return sb.toString();
  }
}