add 1557

fishercoder1534 · fishercoder1534 · commit 3b5d091b349d · 2020-08-22T09:54:53.000-07:00
diff --git a/README.md b/README.md
@@ -8,6 +8,7 @@ _If you like this project, please leave me a star._ &#9733;
 
 |  #  |      Title     |   Solutions   | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|--------|-------------|-------------
+|1557|[Minimum Number of Vertices to Reach All Nodes](https://leetcode.com/problems/minimum-number-of-vertices-to-reach-all-nodes/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1557.java) ||Medium|Graph|
 |1556|[Thousand Separator](https://leetcode.com/problems/thousand-separator/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1556.java) ||Easy|String|
 |1551|[Minimum Operations to Make Array Equal](https://leetcode.com/problems/minimum-operations-to-make-array-equal/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1551.java) | [:tv:](https://youtu.be/A-i2sxmBqAA)|Medium|Math|
 |1550|[Three Consecutive Odds](https://leetcode.com/problems/three-consecutive-odds/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1550.java) | |Easy|Array|
diff --git a/src/main/java/com/fishercoder/solutions/_1557.java b/src/main/java/com/fishercoder/solutions/_1557.java
@@ -0,0 +1,25 @@
+package com.fishercoder.solutions;
+
+import java.util.*;
+
+public class _1557 {
+    public static class Solution1 {
+        public List<Integer> findSmallestSetOfVertices(int n, List<List<Integer>> edges) {
+            List<Integer> starts = new ArrayList<>();
+            Map<Integer, Set<Integer>> indegree = new HashMap<>();
+            for (int i = 0; i < edges.size(); i++) {
+                int end = edges.get(i).get(1);
+                if (!indegree.containsKey(end)) {
+                    indegree.put(end, new HashSet<>());
+                }
+                indegree.get(end).add(edges.get(i).get(0));
+            }
+            for (int i = 0; i < n; i++) {
+                if (!indegree.containsKey(i)) {
+                    starts.add(i);
+                }
+            }
+            return starts;
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_1557Test.java b/src/test/java/com/fishercoder/_1557Test.java
@@ -0,0 +1,33 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._1557;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+public class _1557Test {
+    private static _1557.Solution1 solution1;
+    private static List<List<Integer>> edges;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _1557.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        edges = Arrays.asList(Arrays.asList(0, 1), Arrays.asList(0, 2), Arrays.asList(2, 5), Arrays.asList(3, 4), Arrays.asList(4, 2));
+        assertEquals(Arrays.asList(0, 3), solution1.findSmallestSetOfVertices(6, edges));
+    }
+
+    @Test
+    public void test2() {
+        edges = Arrays.asList(Arrays.asList(0, 1), Arrays.asList(2, 1), Arrays.asList(3, 1), Arrays.asList(1, 4), Arrays.asList(2, 4));
+        assertEquals(Arrays.asList(0, 2, 3), solution1.findSmallestSetOfVertices(5, edges));
+    }
+
+}
