第二周作业#09

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);
+    }
+}

Week_02/id_9/LeetCode_98_9.java

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+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;
+    }
+}