solve 515.在每个树行中找最大值

Author: andavid

zh/515.在每个树行中找最大值.java

@@ -0,0 +1,76 @@
+/*
+ * @lc app=leetcode.cn id=515 lang=java
+ *
+ * [515] 在每个树行中找最大值
+ *
+ * https://leetcode-cn.com/problems/find-largest-value-in-each-tree-row/description/
+ *
+ * algorithms
+ * Medium (60.38%)
+ * Likes:    63
+ * Dislikes: 0
+ * Total Accepted:    11.5K
+ * Total Submissions: 19.1K
+ * Testcase Example:  '[1,3,2,5,3,null,9]'
+ *
+ * 您需要在二叉树的每一行中找到最大的值。
+ *
+ * 示例：
+ *
+ *
+ * 输入:
+ *
+ * ⁠         1
+ * ⁠        / \
+ * ⁠       3   2
+ * ⁠      / \   \
+ * ⁠     5   3   9
+ *
+ * 输出: [1, 3, 9]
+ *
+ *
+ */
+
+// @lc code=start
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+  public List<Integer> largestValues(TreeNode root) {
+    List<Integer> result = new ArrayList<>();
+    if (root == null) {
+      return result;
+    }
+
+    Queue<TreeNode> queue = new LinkedList<>();
+    queue.offer(root);
+
+    while (!queue.isEmpty()) {
+      int size = queue.size();
+      int max = Integer.MIN_VALUE;
+      for (int i = 0; i < size; i++) {
+        TreeNode node = queue.poll();
+        if (node.val > max) {
+          max = node.val;
+        }
+        if (node.left != null) {
+          queue.offer(node.left);
+        }
+        if (node.right != null) {
+          queue.offer(node.right);
+        }
+      }
+      result.add(max);
+    }
+
+    return result;
+  }
+}
+// @lc code=end
+