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| 1 | +package com.leetcode.arrays; |
| 2 | + |
| 3 | +import java.util.ArrayList; |
| 4 | +import java.util.List; |
| 5 | + |
| 6 | +/** |
| 7 | + * Problem: https://leetcode.com/problems/pascals-triangle/ |
| 8 | + * |
| 9 | + * @author rampatra |
| 10 | + * @since 2019年04月20日 |
| 11 | + */ |
| 12 | +public class PascalsTriangle { |
| 13 | + |
| 14 | + /** |
| 15 | + * Time complexity: O(numRows^2) |
| 16 | + * Space complexity: O(numRows^2) |
| 17 | + * <p> |
| 18 | + * Runtime: <a href="https://leetcode.com/submissions/detail/223784377/">0 ms</a>. |
| 19 | + * |
| 20 | + * @param numRows |
| 21 | + * @return |
| 22 | + */ |
| 23 | + public static List<List<Integer>> generatePascalsTriangle(int numRows) { |
| 24 | + List<List<Integer>> pascalsTriangle = new ArrayList<>(); |
| 25 | + |
| 26 | + if (numRows == 0) return pascalsTriangle; |
| 27 | + |
| 28 | + List<Integer> firstRow = new ArrayList<>(); |
| 29 | + firstRow.add(1); |
| 30 | + pascalsTriangle.add(firstRow); |
| 31 | + |
| 32 | + List<Integer> prevRow; |
| 33 | + for (int i = 1; i < numRows; i++) { |
| 34 | + prevRow = pascalsTriangle.get(i - 1); |
| 35 | + |
| 36 | + List<Integer> currRow = new ArrayList<>(); |
| 37 | + currRow.add(1); |
| 38 | + for (int j = 0; j < prevRow.size() - 1; j++) { |
| 39 | + currRow.add(prevRow.get(j) + prevRow.get(j + 1)); |
| 40 | + } |
| 41 | + currRow.add(1); |
| 42 | + |
| 43 | + pascalsTriangle.add(currRow); |
| 44 | + } |
| 45 | + |
| 46 | + return pascalsTriangle; |
| 47 | + } |
| 48 | + |
| 49 | + public static void main(String[] args) { |
| 50 | + System.out.println(generatePascalsTriangle(5)); |
| 51 | + } |
| 52 | +} |
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