Week 02 Homework

cvfghemiao · web-flow · commit 1a4a60a4b903 · 2019-10-27T21:11:53.000+08:00
diff --git a/Week 02/id_331/LeetCode_144_331.java b/Week 02/id_331/LeetCode_144_331.java
@@ -0,0 +1,19 @@
+class Solution {
+    public List<Integer> preorderTraversal(TreeNode root) {
+        List<Integer> res = new ArrayList<>();
+        helper(root, res);
+        return res;
+    }
+    
+    public void helper(TreeNode root, List<Integer> res) {
+        if (root != null) {
+            res.add(root.val);
+            if (root.left != null) {
+                helper(root.left, res);
+            }
+            if (root.right != null) {
+                helper(root.right, res);
+            }
+        }
+    }
+}
diff --git a/Week 02/id_331/LeetCode_242_331.java b/Week 02/id_331/LeetCode_242_331.java
@@ -0,0 +1,19 @@
+class Solution {
+    public boolean isAnagram(String s, String t) {
+        if(s.length() != t.length()) return false;
+        
+        int[] counter = new int[26];
+        for (int i = 0; i < s.length(); i++) {
+            counter[s.charAt(i) - 'a']++; 
+        }
+        
+        for (int i = 0; i < t.length(); i++) {
+            counter[t.charAt(i) - 'a']--;
+            if(counter[t.charAt(i) - 'a'] < 0){
+                return false;
+            }
+        }
+        
+        return true;
+    }
+}
diff --git a/Week 02/id_331/LeetCode_49_331.java b/Week 02/id_331/LeetCode_49_331.java
@@ -0,0 +1,20 @@
+class Solution {
+    public List<List<String>> groupAnagrams(String[] strs) {
+        if (strs.length == 0) {
+            return new ArrayList<>();
+        }
+        
+        Map<String, List<String>> ans = new HashMap<>();
+        
+        for (String str : strs) {
+            char[] ch = str.toCharArray();
+            Arrays.sort(ch);
+            String key = String.valueOf(ch);
+            if (!ans.containsKey(key)) {
+                ans.put(key, new ArrayList<>());
+            }
+            ans.get(key).add(str);
+        }
+        return new ArrayList<>(ans.values());
+    }
+}
diff --git a/Week 02/id_331/LeetCode_94_331.java b/Week 02/id_331/LeetCode_94_331.java
@@ -0,0 +1,28 @@
+/**
+ * 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> inorderTraversal(TreeNode root) {
+        List<Integer> res = new ArrayList<>();
+        helper(root, res);
+        return res;
+    }
+    
+    public void helper(TreeNode root, List<Integer> res) {
+        if (root != null) {
+            if (root.left != null) {
+                helper(root.left, res);
+            }
+            res.add(root.val);
+            if (root.right != null) {
+                helper(root.right, res);
+            }
+        }
+    }
+}
