solve 119.pascals-triangle-ii

Author: andavid

vscode/119.pascals-triangle-ii.java

@@ -0,0 +1,49 @@
+/*
+ * @lc app=leetcode id=119 lang=java
+ *
+ * [119] Pascal's Triangle II
+ *
+ * https://leetcode.com/problems/pascals-triangle-ii/description/
+ *
+ * algorithms
+ * Easy (42.10%)
+ * Total Accepted:    195.6K
+ * Total Submissions: 455.8K
+ * Testcase Example:  '3'
+ *
+ * Given a non-negative index k where k ≤ 33, return the k^th index row of the
+ * Pascal's triangle.
+ *
+ * Note that the row index starts from 0.
+ *
+ *
+ * In Pascal's triangle, each number is the sum of the two numbers directly
+ * above it.
+ *
+ * Example:
+ *
+ *
+ * Input: 3
+ * Output: [1,3,3,1]
+ *
+ *
+ * Follow up:
+ *
+ * Could you optimize your algorithm to use only O(k) extra space?
+ *
+ */
+class Solution {
+  public List<Integer> getRow(int rowIndex) {
+    List<Integer> result = new ArrayList<>();
+    if (rowIndex < 0) return result;
+    result.add(1);
+    for (int i = 1; i <= rowIndex; i++) {
+      for (int j = i - 1; j > 0; j--) {
+        result.set(j, result.get(j) + result.get(j-1));
+      }
+      result.add(1);
+    }
+    return result;
+  }
+}
+