6 - Zigzag Conversion

 JAVA

• class Solution {
      public String convert(String s, int numRows) {
          if (numRows == 1) {
              return s;
          }
          StringBuilder ans = new StringBuilder();
          int group = 2 * numRows - 2;
          for (int i = 1; i <= numRows; i++) {
              int interval = i == numRows ? group : 2 * numRows - 2 * i;
              int idx = i - 1;
              while (idx < s.length()) {
                  ans.append(s.charAt(idx));
                  idx += interval;
                  interval = group - interval;
                  if (interval == 0) {
                      interval = group;
                  }
              }
          }
          return ans.toString();
      }
  }

C++

• class Solution {
  public:
      string convert(string s, int numRows) {
          if (numRows == 1) return s;
          string ans;
          int group = 2 * numRows - 2;
          for (int i = 1; i <= numRows; ++i) {
              int interval = i == numRows ? group : 2 * numRows - 2 * i;
              int idx = i - 1;
              while (idx < s.length()) {
                  ans.push_back(s[idx]);
                  idx += interval;
                  interval = group - interval;
                  if (interval == 0) interval = group;
              }
          }
          return ans;
      }
  };