add a solution for 404

Author: fishercoder1534

src/main/java/com/fishercoder/solutions/_404.java

@@ -2,6 +2,9 @@
 
 import com.fishercoder.common.classes.TreeNode;
 
+import java.util.LinkedList;
+import java.util.Queue;
+
 public class _404 {
     public static class Solution1 {
         public int sumOfLeftLeaves(TreeNode root) {
@@ -51,4 +54,33 @@ public int sumOfLeftLeaves(TreeNode root) {
             return sum;
         }
     }
+
+    public static class Solution3 {
+        /**
+         * My completely original solution on 11/4/2021.
+         */
+        public int sumOfLeftLeaves(TreeNode root) {
+            Queue<TreeNode> queue = new LinkedList<>();
+            queue.offer(root);
+            int level = 0;
+            int sum = 0;
+            while (!queue.isEmpty()) {
+                int size = queue.size();
+                for (int i = 0; i < size; i++) {
+                    TreeNode curr = queue.poll();
+                    if (curr == null) {
+                        continue;
+                    }
+                    if (level > 0 && curr.left == null && curr.right == null && i % 2 != 1) {
+                        sum += curr.val;
+                    }
+                    queue.offer(curr.left);
+                    queue.offer(curr.right);
+
+                }
+                level++;
+            }
+            return sum;
+        }
+    }
 }

src/test/java/com/fishercoder/_404Test.java

@@ -0,0 +1,45 @@
+package com.fishercoder;
+
+import com.fishercoder.common.classes.TreeNode;
+import com.fishercoder.common.utils.TreeUtils;
+import com.fishercoder.solutions._404;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.Arrays;
+
+import static junit.framework.TestCase.assertEquals;
+
+public class _404Test {
+    private static _404.Solution1 solution1;
+    private static _404.Solution2 solution2;
+    private static _404.Solution3 solution3;
+    private static TreeNode root;
+    private static int expected;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _404.Solution1();
+        solution2 = new _404.Solution2();
+        solution3 = new _404.Solution3();
+    }
+
+    @Test
+    public void test1() {
+        root = TreeUtils.constructBinaryTree(Arrays.asList(3, 9, 20, null, null, 15, 7));
+        expected = 24;
+        assertEquals(expected, solution1.sumOfLeftLeaves(root));
+        assertEquals(expected, solution2.sumOfLeftLeaves(root));
+        assertEquals(expected, solution3.sumOfLeftLeaves(root));
+    }
+
+    @Test
+    public void test2() {
+        root = TreeUtils.constructBinaryTree(Arrays.asList(1, null, 2));
+        expected = 0;
+        assertEquals(expected, solution1.sumOfLeftLeaves(root));
+        assertEquals(expected, solution2.sumOfLeftLeaves(root));
+        assertEquals(expected, solution3.sumOfLeftLeaves(root));
+    }
+
+}