_119.java

package com.fishercoder.solutions;

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

/**
 * 119. Pascal's Triangle II
 * Given an index k, return the kth row of the Pascal's triangle.

 For example, given k = 3,
 Return [1,3,3,1].

 Note:
 Could you optimize your algorithm to use only O(k) extra space?
 */

public class _119 {

  public static class Solution1 {
    public List<Integer> getRow(int rowIndex) {
      if (rowIndex < 0) {
        return new ArrayList();
      }
      List<List<Integer>> result = new ArrayList();
      List<Integer> row = new ArrayList();
      row.add(1);
      result.add(row);
      for (int i = 1; i <= rowIndex; i++) {
        List<Integer> newRow = new ArrayList();
        newRow.add(1);
        List<Integer> lastRow = result.get(i - 1);
        for (int j = 1; j < lastRow.size(); j++) {
          newRow.add(lastRow.get(j - 1) + lastRow.get(j));
        }
        newRow.add(1);
        result.add(newRow);
      }
      return result.get(result.size() - 1);
    }
  }

  public static class Solution2 {
    /** O(k) space */
    public List<Integer> getRow(int rowIndex) {
      List<Integer> row = new ArrayList<>();
      for (int i = 0; i <= rowIndex; i++) {
        row.add(0, 1);
        for (int j = 1; j < row.size() - 1; j++) {
          row.set(j, row.get(j) + row.get(j + 1));
        }
      }
      return row;
    }
  }
}