add 1018

fishercoder1534 · fishercoder1534 · commit c431845afc35 · 2019-04-06T10:22:20.000-07:00
diff --git a/README.md b/README.md
@@ -27,6 +27,7 @@ Your ideas/fixes/algorithms are more than welcome!
 
 |  #  |      Title     |   Solutions   | Time          | Space         | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|---------------|---------------|--------|-------------|-------------
+|1018|[Binary Prefix Divisible By 5](https://leetcode.com/problems/binary-prefix-divisible-by-5/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1018.java) | O(n) | O(1) | |Easy|
 |1013|[Pairs of Songs With Total Durations Divisible by 60](https://leetcode.com/problems/pairs-of-songs-with-total-durations-divisible-by-60/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1013.java) | O(n) | O(1) | |Easy|
 |1002|[Find Common Characters](https://leetcode.com/problems/find-common-characters/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1002.java) | O(n) | O(1) | |Easy|
 |999|[Available Captures for Rook](https://leetcode.com/problems/available-captures-for-rook/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_999.java) | O(1) | O(1) | |Easy|
diff --git a/src/main/java/com/fishercoder/solutions/_1018.java b/src/main/java/com/fishercoder/solutions/_1018.java
@@ -0,0 +1,52 @@
+package com.fishercoder.solutions;
+
+import java.math.BigInteger;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 1018. Binary Prefix Divisible By 5
+ *
+ * Given an array A of 0s and 1s, consider N_i: the i-th subarray from A[0] to A[i] interpreted as a binary number (from most-significant-bit to least-significant-bit.)
+ *
+ * Return a list of booleans answer, where answer[i] is true if and only if N_i is divisible by 5.
+ *
+ * Example 1:
+ *
+ * Input: [0,1,1]
+ * Output: [true,false,false]
+ * Explanation:
+ * The input numbers in binary are 0, 01, 011; which are 0, 1, and 3 in base-10.  Only the first number is divisible by 5, so answer[0] is true.
+ * Example 2:
+ *
+ * Input: [1,1,1]
+ * Output: [false,false,false]
+ * Example 3:
+ *
+ * Input: [0,1,1,1,1,1]
+ * Output: [true,false,false,false,true,false]
+ * Example 4:
+ *
+ * Input: [1,1,1,0,1]
+ * Output: [false,false,false,false,false]
+ *
+ *
+ * Note:
+ *
+ * 1 <= A.length <= 30000
+ * A[i] is 0 or 1
+ * */
+public class _1018 {
+    public static class Solution1 {
+        /**credit: https://leetcode.com/problems/binary-prefix-divisible-by-5/discuss/266051/Java-beats-100*/
+        public List<Boolean> prefixesDivBy5(int[] A) {
+            List<Boolean> result = new ArrayList<>(A.length);
+            int remainder = 0;
+            for (int a : A) {
+                remainder = ((remainder << 1) + a) % 5;
+                result.add(remainder == 0);
+            }
+            return result;
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_1018Test.java b/src/test/java/com/fishercoder/_1018Test.java
@@ -0,0 +1,50 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._1018;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.Arrays;
+
+import static junit.framework.Assert.assertEquals;
+
+public class _1018Test {
+    private static _1018.Solution1 solution1;
+    private static int[] A;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _1018.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        A = new int[]{0, 1, 1};
+        assertEquals(Arrays.asList(true, false, false), solution1.prefixesDivBy5(A));
+    }
+
+    @Test
+    public void test2() {
+        A = new int[]{1, 1, 1};
+        assertEquals(Arrays.asList(false, false, false), solution1.prefixesDivBy5(A));
+    }
+
+    @Test
+    public void test3() {
+        A = new int[]{0, 1, 1, 1, 1, 1};
+        assertEquals(Arrays.asList(true, false, false, false, true, false), solution1.prefixesDivBy5(A));
+    }
+
+    @Test
+    public void test4() {
+        A = new int[]{1, 1, 1, 0, 1};
+        assertEquals(Arrays.asList(false, false, false, false, false), solution1.prefixesDivBy5(A));
+    }
+
+    @Test
+    public void test5() {
+        A = new int[]{1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 1};
+        assertEquals(Arrays.asList(false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, true, false, false, true, true, true, true, false), solution1.prefixesDivBy5(A));
+    }
+
+}
