From d4d3dc03a9fdf96f96f4feb0f1ff3487ff53573f Mon Sep 17 00:00:00 2001
From: Nezuko-Wen <409053122@qq.com>
Date: Sat, 5 Dec 2020 11:39:14 +0800
Subject: [PATCH] =?UTF-8?q?dfs=E6=89=BE=E5=A5=BD=E5=8F=B6=E5=AD=90?=
 =?UTF-8?q?=E8=8A=82=E7=82=B9=E5=AF=B9?=
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---
 src/leecode/tree/No1530.java | 52 ++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 src/leecode/tree/No1530.java

diff --git a/src/leecode/tree/No1530.java b/src/leecode/tree/No1530.java
new file mode 100644
index 0000000..484287e
--- /dev/null
+++ b/src/leecode/tree/No1530.java
@@ -0,0 +1,52 @@
+package leecode.tree;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * 给你二叉树的根节点 root 和一个整数 distance 。
+ *
+ * 如果二叉树中两个 叶 节点之间的 最短路径长度 小于或者等于 distance ，那它们就可以构成一组 好叶子节点对 。
+ *
+ * 返回树中 好叶子节点对的数量
+ *
+ * 来源：力扣（LeetCode）
+ * 链接：https://leetcode-cn.com/problems/number-of-good-leaf-nodes-pairs
+ */
+public class No1530 {
+    private int ret = 0;
+
+    public int countPairs(TreeNode root, int distance) {
+        dfs(root, distance);
+        return ret;
+    }
+
+    private List<Integer> dfs(TreeNode root, int distance) {
+        if (root == null) return null;
+        if (root.left == null && root.right == null) return Collections.singletonList(0);
+        List<Integer> dfsOnce = new ArrayList<>();
+        List<Integer> leftArr = dfs(root.left, distance);
+        List<Integer> rightArr = dfs(root.right, distance);
+        if (root.left != null) {
+            for (int l : leftArr) {
+                if (++l > distance) continue;
+                dfsOnce.add(l);
+            }
+        }
+        if (root.right != null) {
+            for (int r : rightArr) {
+                if (++r > distance) continue;
+                dfsOnce.add(r);
+            }
+        }
+        if (root.left != null && root.right != null) {
+            for (int l : leftArr) {
+                for (int r : rightArr) {
+                    if (l + r + 2 <= distance) ret++;
+                }
+            }
+        }
+        return dfsOnce;
+    }
+}