add: WidestBinaryTreeLevel

Author: Jer3myYu

java/Trees/WidestBinaryTreeLevel.java

@@ -0,0 +1,60 @@
+import java.util.ArrayDeque;
+import java.util.Queue;
+
+import DS.TreeNode;
+
+/*
+    // Definition of TreeNode:
+    class TreeNode {
+        public int val;
+        public TreeNode left;
+        public TreeNode right;
+        public TreeNode(int val) {
+            this.val = val;
+        }
+    }
+ */
+
+public class WidestBinaryTreeLevel {
+    public class Pair {
+        TreeNode node;
+        int index;
+        public Pair(TreeNode node, int index) {
+            this.node = node;
+            this.index = index;
+        }
+    }
+
+    public int widestBinaryTreeLevel(TreeNode root) {
+        if (root == null) {
+            return 0;
+        }
+        int maxWidth = 0;
+        Queue<Pair> queue = new ArrayDeque<>();
+        queue.offer(new Pair(root, 0)); // Stores (node, index) pairs.
+        while (!queue.isEmpty()) {
+            int levelSize = queue.size();
+            // Set the 'leftmostIndex' to the index of the first node in 
+            // this level. Start 'rightmostIndex' at the same point as 
+            // 'leftmostIndex' and update it as we traverse the level, 
+            // eventually positioning it at the last node.
+            int leftmostIndex = queue.peek().index;
+            int rightmostIndex = leftmostIndex;
+            // Process all nodes at the current level.
+            for (int j = 0; j < levelSize; j++) {
+                Pair pair = queue.poll();
+                TreeNode node = pair.node;
+                int i = pair.index;
+                if (node.left != null) {
+                    queue.offer(new Pair(node.left, 2 * i + 1));
+                }
+                if (node.right != null) {
+                    queue.offer(new Pair(node.right, 2 * i + 2));
+                }
+                rightmostIndex = i;
+            }
+            maxWidth = Math.max(maxWidth, rightmostIndex - leftmostIndex + 1);
+        }
+        return maxWidth;
+    }
+}