From c6ffd4f04f2afe4543a3a1c2168b804a2a414178 Mon Sep 17 00:00:00 2001
From: bky373 <bo373@naver.com>
Date: Mon, 3 Jun 2024 22:13:30 +0900
Subject: [PATCH] Solve week 4 problems

---
 counting-bits/bky373.java    | 23 +++++++++++++++++++++++
 group-anagrams/bky373.java   | 19 +++++++++++++++++++
 missing-number/bky373.java   | 15 +++++++++++++++
 number-of-1-bits/bky373.java | 17 +++++++++++++++++
 reverse-bits/bky373.java     | 17 +++++++++++++++++
 5 files changed, 91 insertions(+)
 create mode 100644 counting-bits/bky373.java
 create mode 100644 group-anagrams/bky373.java
 create mode 100644 missing-number/bky373.java
 create mode 100644 number-of-1-bits/bky373.java
 create mode 100644 reverse-bits/bky373.java

diff --git a/counting-bits/bky373.java b/counting-bits/bky373.java
new file mode 100644
index 000000000..27a6e59f8
--- /dev/null
+++ b/counting-bits/bky373.java
@@ -0,0 +1,23 @@
+/**
+ * https://leetcode.com/problems/counting-bits/
+ *
+ * time: O(n * log n)
+ * space: O(1)
+ */
+class Solution {
+
+    public int[] countBits(int n) {
+        int[] ans = new int[n + 1];
+        for (int i = 0; i <= n; i++) {
+            int x = i;
+            int cnt = 0;
+            while (x != 0) {
+                cnt++;
+                x &= (x - 1);
+            }
+            ans[i] = cnt;
+        }
+        return ans;
+    }
+}
+
diff --git a/group-anagrams/bky373.java b/group-anagrams/bky373.java
new file mode 100644
index 000000000..bde289cba
--- /dev/null
+++ b/group-anagrams/bky373.java
@@ -0,0 +1,19 @@
+/**
+ * https://leetcode.com/problems/group-anagrams/
+ *
+ * time: O(n * m log m)
+ * space: O(nm)
+ */
+class Solution {
+
+    public List<List<String>> groupAnagrams(String[] strs) {
+        Map<String, List<String>> groups = new HashMap();
+        for (String str : strs) {
+            char[] arr = str.toCharArray();
+            Arrays.sort(arr);
+            groups.computeIfAbsent(new String(arr), k -> new ArrayList<>())
+                  .add(str);
+        }
+        return new ArrayList(groups.values());
+    }
+}
diff --git a/missing-number/bky373.java b/missing-number/bky373.java
new file mode 100644
index 000000000..07d2fe998
--- /dev/null
+++ b/missing-number/bky373.java
@@ -0,0 +1,15 @@
+/**
+ * https://leetcode.com/problems/missing-number/
+ *
+ * time: O(n)
+ * space: O(1)
+ */
+class Solution {
+    public int missingNumber(int[] nums) {
+        int sum = nums.length * (nums.length+1) / 2;
+        for (int num : nums) {
+            sum -= num;
+        }
+        return sum;
+    }
+}
diff --git a/number-of-1-bits/bky373.java b/number-of-1-bits/bky373.java
new file mode 100644
index 000000000..ff4d40612
--- /dev/null
+++ b/number-of-1-bits/bky373.java
@@ -0,0 +1,17 @@
+/**
+ * https://leetcode.com/problems/number-of-1-bits/
+ *
+ * time: O(log n)
+ * space: O(1)
+ */
+class Solution {
+
+    public int hammingWeight(int n) {
+        int cnt = 0;
+        while (n != 0) {
+            cnt++;
+            n &= (n - 1);
+        }
+        return cnt;
+    }
+}
diff --git a/reverse-bits/bky373.java b/reverse-bits/bky373.java
new file mode 100644
index 000000000..ddad6ded5
--- /dev/null
+++ b/reverse-bits/bky373.java
@@ -0,0 +1,17 @@
+/**
+ * https://leetcode.com/problems/reverse-bits/
+ *
+ * time: O(1)
+ * space: O(1)
+ */
+public class Solution {
+
+    public int reverseBits(int n) {
+        int ans = 0;
+        for (int i = 0; i < 32; i++) {
+            ans = ans << 1 | n & 1;
+            n >>= 1;
+        }
+        return ans;
+    }
+}