第一周作业#33

Week_01/id_33/LeetCode_101_033.java

@@ -0,0 +1,28 @@
+/*
+ * @lc app=leetcode id=101 lang=java
+ *
+ * [101] Symmetric Tree
+ */
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public boolean isSymmetric(TreeNode root) {
+        return isSym(root, root);
+    }
+
+    public boolean isSym(TreeNode leftNode, TreeNode rightNode) {
+        if(leftNode == null && rightNode == null)
+            return true;
+        if(leftNode == null || rightNode == null || leftNode.val != rightNode.val)
+            return false;
+        return isSym(leftNode.left, rightNode.right) && isSym(leftNode.right, rightNode.left);
+    }
+}
+

Week_01/id_33/LeetCode_104_033.java

@@ -0,0 +1,24 @@
+/*
+ * @lc app=leetcode id=104 lang=java
+ *
+ * [104] Maximum Depth of Binary Tree
+ */
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public int maxDepth(TreeNode root) {
+        if(root == null)
+            return 0;
+        int leftMaxDepth = maxDepth(root.left);
+        int rightMaxDepth = maxDepth(root.right);
+        return Math.max(leftMaxDepth, rightMaxDepth) + 1;
+    }
+}
+

Week_01/id_33/LeetCode_24_033.java

@@ -0,0 +1,34 @@
+/*
+ * @lc app=leetcode id=24 lang=java
+ *
+ * [24] Swap Nodes in Pairs
+ */
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public ListNode swapPairs(ListNode head) {
+        ListNode pre = new ListNode(0);
+        ListNode cur = head;
+        pre.next = head;
+        ListNode tmp = pre;
+        while(cur != null){
+            ListNode next = cur.next;
+            if(next != null){
+                cur.next = next.next;
+                next.next = cur;
+                pre.next = next;
+                pre = cur;
+                cur = cur.next;
+            } else 
+                break;
+        }
+        return tmp.next;
+    }
+}
+

Week_01/id_33/LeetCode_26_033.java

@@ -0,0 +1,21 @@
+/*
+ * @lc app=leetcode id=26 lang=java
+ *
+ * [26] Remove Duplicates from Sorted Array
+ */
+class Solution {
+    public int removeDuplicates(int[] nums) {
+        int len = nums.length;
+        if(len == 0)
+            return 0;
+        int cur = 0;
+        for(int i = 0; i < len; i++){
+            if(nums[i] != nums[cur]){
+                cur++;
+                nums[cur] = nums[i];
+            }
+        }
+        return cur + 1;
+    }
+}
+

Week_01/id_33/LeetCode_49_033.java

@@ -0,0 +1,23 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+
+/*
+ * @lc app=leetcode id=49 lang=java
+ *
+ * [49] Group Anagrams
+ */
+class Solution {
+    public List<List<String>> groupAnagrams(String[] strs) {
+        Map<String, List<String>> sortedMap = new HashMap<>();
+        for (String word : strs) {
+            char[] charWord = word.toCharArray();
+            Arrays.sort(charWord);
+            String newStr = new String(charWord);
+            sortedMap.putIfAbsent(newStr,new ArrayList<>());
+            sortedMap.get(newStr).add(word);
+        }
+        return new ArrayList<>(sortedMap.values());
+    }
+}
+

Week_01/id_33/LeetCode_50_033.java

@@ -0,0 +1,19 @@
+/*
+ * @lc app=leetcode id=50 lang=java
+ *
+ * [50] Pow(x, n)
+ */
+class Solution {
+    public double myPow(double x, int n) {
+        if(n == 0)
+            return 1;
+        if(n == 1)
+            return x;
+        double half = myPow(x, n/2);
+        if(n % 2 == 0)
+            return half * half;
+        else
+            return n > 0 ? half * half * x : half * half * (1/x); 
+    }
+}
+