_118.java

package com.fishercoder.solutions;

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

/**
 * 118. Pascal's Triangle
 * Given numRows, generate the first numRows of Pascal's triangle.

 For example, given numRows = 5,
 Return

 [
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
 ]

 */
public class _118 {

  public static class Solution1 {
    /**fill out values from left to right*/
    public List<List<Integer>> generate(int numRows) {
      List<List<Integer>> result = new ArrayList();
      List<Integer> row = new ArrayList();
      for (int i = 0; i < numRows; i++) {
        row.add(0, 1);
        for (int j = 1; j < row.size() - 1; j++) {
          row.set(j, row.get(j) + row.get(j + 1));
        }
        result.add(new ArrayList(row));
      }
      return result;
    }
  }

  public static class Solution2 {
    /**fill out values from right to left
     * credit: https://leetcode.com/problems/pascals-triangle/discuss/38141/My-concise-solution-in-Java/36127*/
    public List<List<Integer>> generate(int numRows) {
      List<List<Integer>> result = new ArrayList();
      List<Integer> row = new ArrayList();
      for (int i = 0; i < numRows; i++) {
        for (int j = row.size() - 1; j >= 1; j--) {
          row.set(j, row.get(j) + row.get(j - 1));
        }
        row.add(1);
        result.add(new ArrayList<>(row));
      }
      return result;
    }
  }
}