PascalsTriangle.java

/* (C) 2024 YourCompanyName */
package array;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * Created by gouthamvidyapradhan on 25/03/2017.
 *
 * <p>Given an index k, return the kth row of the Pascal's triangle.
 *
 * <p>For example, given k = 3, Return [1,3,3,1].
 *
 * <p>Note: Could you optimize your algorithm to use only O(k) extra space?
 */
public class PascalsTriangle {
  public static void main(String[] args) throws Exception {
    System.out.println(new PascalsTriangle().getRow(3));
  }

  public List<Integer> getRow(int rowIndex) {
    int k = rowIndex;
    if (k == 0) return Arrays.asList(1);
    else if (k == 1) return Arrays.asList(1, 1);
    else if (k == 2) return Arrays.asList(1, 2, 1);
    List<Integer> result = new ArrayList<>();
    result.add(2);
    k = k - 2;
    int p, c;
    while (k-- > 0) {
      p = 1;
      int i = 0;
      for (int l = result.size(); i < l; i++) {
        c = result.get(i);
        result.set(i, p + c);
        p = c;
      }
      result.add(p + 1);
    }
    result.add(0, 1);
    result.add(1);
    return result;
  }
}