add 1361

fishercoder1534 · fishercoder1534 · commit 25f9fbca4084 · 2020-02-23T04:36:51.000-08:00
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                   
 |-----|----------------|---------------|--------|-------------|-------------
+|1361|[Validate Binary Tree Nodes](https://leetcode.com/problems/validate-binary-tree-nodes/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1361.java) | |Medium||Graph
 |1360|[Number of Days Between Two Dates](https://leetcode.com/problems/number-of-days-between-two-dates/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1360.java) | |Easy||
 |1358|[Number of Substrings Containing All Three Characters](https://leetcode.com/problems/number-of-substrings-containing-all-three-characters/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1358.java) | |Medium|String|
 |1357|[Apply Discount Every n Orders](https://leetcode.com/problems/apply-discount-every-n-orders/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1357.java) | |Medium|Design|
diff --git a/src/main/java/com/fishercoder/solutions/_1361.java b/src/main/java/com/fishercoder/solutions/_1361.java
@@ -0,0 +1,81 @@
+package com.fishercoder.solutions;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * 1361. Validate Binary Tree Nodes
+ *
+ * You have n binary tree nodes numbered from 0 to n - 1 where node i has two children leftChild[i] and rightChild[i],
+ * return true if and only if all the given nodes form exactly one valid binary tree.
+ * If node i has no left child then leftChild[i] will equal -1, similarly for the right child.
+ * Note that the nodes have no values and that we only use the node numbers in this problem.
+ *
+ * Example 1:
+ * Input: n = 4, leftChild = [1,-1,3,-1], rightChild = [2,-1,-1,-1]
+ * Output: true
+ *
+ * Example 2:
+ * Input: n = 4, leftChild = [1,-1,3,-1], rightChild = [2,3,-1,-1]
+ * Output: false
+ *
+ * Example 3:
+ * Input: n = 2, leftChild = [1,0], rightChild = [-1,-1]
+ * Output: false
+ *
+ * Example 4:
+ * Input: n = 6, leftChild = [1,-1,-1,4,-1,-1], rightChild = [2,-1,-1,5,-1,-1]
+ * Output: false
+ *
+ * Constraints:
+ * 1 <= n <= 10^4
+ * leftChild.length == rightChild.length == n
+ * -1 <= leftChild[i], rightChild[i] <= n - 1
+ * */
+public class _1361 {
+    public static class Solution1 {
+        public boolean validateBinaryTreeNodes(int n, int[] leftChild, int[] rightChild) {
+            int[] indegree = new int[n];
+            for (int i = 0; i < n; i++) {
+                if (leftChild[i] >= 0) {
+                    indegree[leftChild[i]]++;
+                }
+                if (rightChild[i] >= 0) {
+                    indegree[rightChild[i]]++;
+                }
+            }
+            //only one node has in-degree = 0
+            int indegreeZero = 0;
+            for (int num : indegree) {
+                if (num == 0) {
+                    indegreeZero++;
+                    if (indegreeZero > 1) {
+                        return false;
+                    }
+                }
+                //every other node's in-degree must be exactly equal to 1
+                if (num > 1) {
+                    return false;
+                }
+            }
+            //no bi-directional pointing
+            Map<Integer, List<Integer>> map = new HashMap<>();
+            for (int i = 0; i < n; i++) {
+                map.put(i, new ArrayList<>());
+                map.get(i).add(leftChild[i]);
+                map.get(i).add(rightChild[i]);
+            }
+            for (int node : map.keySet()) {
+                List<Integer> children = map.get(node);
+                for (int child : children) {
+                    if (map.containsKey(child) && map.get(child).contains(node)) {
+                        return false;
+                    }
+                }
+            }
+            return true;
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_1361Test.java b/src/test/java/com/fishercoder/_1361Test.java
@@ -0,0 +1,37 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._1361;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _1361Test {
+    private static _1361.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _1361.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(true, solution1.validateBinaryTreeNodes(4, new int[]{1, -1, 3, -1}, new int[]{2, -1, -1, -1}));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals(false, solution1.validateBinaryTreeNodes(4, new int[]{1, -1, 3, -1}, new int[]{2, 3, -1, -1}));
+    }
+
+    @Test
+    public void test3() {
+        assertEquals(false, solution1.validateBinaryTreeNodes(2, new int[]{1, 0}, new int[]{-1, -1}));
+    }
+
+    @Test
+    public void test4() {
+        assertEquals(false, solution1.validateBinaryTreeNodes(6, new int[]{1, -1, -1, 4, -1, -1}, new int[]{2, -1, -1, 5, -1, -1}));
+    }
+
+}
