Add Reverse Bits, Single Number, Happy Number C#

Author: hellomrsun

30-Day-Leetcoding-Challenge/01-Single-Number/Single-Number.cs

@@ -0,0 +1,23 @@
+public class Solution {
+    //XOR solution
+    public int SingleNumber(int[] nums) {
+        var result = 0;
+        for(int i=0; i<nums.Length; i++){
+            result ^= nums[i];
+        }
+        return result;
+    }
+    
+    //Dictionary solution
+    public int SingleNumber(int[] nums) {
+        var dict = new Dictionary<int, int>();
+        for(int i=0; i<nums.Length; i++){
+            if(!dict.ContainsKey(nums[i])){
+                dict.Add(nums[i], 1);
+            }else{
+                dict[nums[i]]++;
+            }
+        }
+        return dict.First(x => x.Value == 1).Key;   
+    }
+}

30-Day-Leetcoding-Challenge/02-Happy-Number/Happy-Number.cs

@@ -0,0 +1,29 @@
+public class Solution
+{
+    public bool IsHappy(int n)
+    {
+        var hs = new HashSet<int>();
+        var left = 0;
+        //HashSet is the key
+        while (hs.Add(n))
+        {
+            var sum = 0;
+            while (n > 0)
+            {
+                left = n % 10;
+                sum += left * left;
+                n /= 10;
+            }
+
+            if (sum == 1)
+            {
+                return true;
+            }
+            else
+            {
+                n = sum;
+            }
+        }
+        return false;
+    }
+}

July-LeetCoding-Challenge/12-Reverse-Bits/Reverse-Bits.cs

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+public class Solution
+{
+
+    //Bitwise solution
+    public uint reverseBits(uint n) {
+        if(n == 0) return 0;
+        uint result = 0;
+        for(int i=0; i<32; i++){
+            result <<= 1;
+            if((n & 1) == 1) result++;
+            n >>= 1;
+        }
+        return result;
+    }
+
+
+    //Stack solution
+    public uint reverseBits(uint n)
+    {
+        //Push to stack
+        var stack = new Stack<uint>();
+        while (n > 0)
+        {
+            stack.Push(n % 2);
+            n = n / 2;
+        }
+
+        //Fill empty slots
+        var length = stack.Count;
+        if (length < 32)
+        {
+            var tl = 32 - length;
+            for (int i = 0; i < tl; i++)
+            {
+                stack.Push(0);
+            }
+        }
+
+        //Construct number
+        uint b = 1;
+        uint result = 0;
+        if (stack.Pop() == 0) result = 0;
+        else result = 1;
+        while (stack.Count > 0)
+        {
+            b *= 2;
+            var r = stack.Pop();
+            result = result + b * r;
+        }
+
+        return result;
+    }
+}