From 7b9990113e41a1c7f05616caaacc64ea6bfb91c5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=9D=8E=E4=BC=9F=E8=B6=85?= <liweichao0102@gmail.com>
Date: Sun, 16 Jun 2019 22:22:00 +0800
Subject: [PATCH] =?UTF-8?q?feat(=E4=BD=9C=E4=B8=9A):=20=E7=AC=AC=E4=BA=8C?=
 =?UTF-8?q?=E5=91=A8=E4=BD=9C=E4=B8=9A?=
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---
 Week_02/id_9/LeetCode_242_9.java | 67 ++++++++++++++++++++++++++++++++
 Week_02/id_9/LeetCode_98_9.java  | 29 ++++++++++++++
 2 files changed, 96 insertions(+)
 create mode 100644 Week_02/id_9/LeetCode_242_9.java
 create mode 100644 Week_02/id_9/LeetCode_98_9.java

diff --git a/Week_02/id_9/LeetCode_242_9.java b/Week_02/id_9/LeetCode_242_9.java
new file mode 100644
index 00000000..9782a887
--- /dev/null
+++ b/Week_02/id_9/LeetCode_242_9.java
@@ -0,0 +1,67 @@
+package com.github.lifelab.leetcode.problemset;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * 有效的字母异位词 @see https://leetcode-cn.com/problems/valid-anagram/
+ *
+ * @author Weichao Li (liweichao0102@gmail.com)
+ * @since 2019-06-16
+ */
+public class Solution242 {
+
+    public boolean isAnagram(String s, String t) {
+        if (Objects.isNull(s) || Objects.isNull(t)) {
+            return false;
+        }
+        if (s.length() != t.length()) {
+            return false;
+        }
+
+        char[] temp = new char[26];
+
+        for (int i = 0; i < s.length(); i++) {
+            temp[s.charAt(i) - 'a']++;
+            temp[t.charAt(i) - 'a']--;
+        }
+
+        for (int i = 0; i < temp.length; i++) {
+            if (temp[i] != 0) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    public boolean isAnagram1(String s, String t) {
+        if (Objects.isNull(s) || Objects.isNull(t)) {
+            return false;
+        }
+        if (s.length() != t.length()) {
+            return false;
+        }
+        char[] sarray = s.toCharArray();
+        char[] tarray = t.toCharArray();
+        Arrays.sort(sarray);
+        Arrays.sort(tarray);
+        return Arrays.equals(sarray, tarray);
+    }
+
+    public boolean isAnagram2(String s, String t) {
+        if (Objects.isNull(s) || Objects.isNull(t)) {
+            return false;
+        }
+        if (s.length() != t.length()) {
+            return false;
+        }
+        Map<Character, Integer> maps = new HashMap<>(t.length());
+        for (int i = 0; i < s.length(); i++) {
+            maps.compute(s.charAt(i), (k, v) -> maps.getOrDefault(k, 0) + 1);
+            maps.compute(t.charAt(i), (k, v) -> maps.getOrDefault(k, 0) - 1);
+        }
+        return maps.values().stream().parallel().allMatch(e -> Objects.isNull(e) | e == 0);
+    }
+}
\ No newline at end of file
diff --git a/Week_02/id_9/LeetCode_98_9.java b/Week_02/id_9/LeetCode_98_9.java
new file mode 100644
index 00000000..d323c83b
--- /dev/null
+++ b/Week_02/id_9/LeetCode_98_9.java
@@ -0,0 +1,29 @@
+package com.github.lifelab.leetcode.problemset;
+
+/**
+ * 验证二叉搜索树 @see https://leetcode-cn.com/problems/validate-binary-search-tree/submissions/
+ *
+ * @author Weichao Li (liweichao0102@gmail.com)
+ * @since 2019-06-16
+ */
+public class Solution98 {
+
+    long temp = Long.MIN_VALUE;
+
+    public boolean isValidBST(TreeNode root) {
+        //terminator
+        if (root == null) {
+            return true;
+        }
+
+        // process
+        if (isValidBST(root.left)) {
+            if (temp < root.val) {
+                temp = root.val;
+                //drill down
+                return isValidBST(root.right);
+            }
+        }
+        return false;
+    }
+}