tested on leetcode;

FindCelebrityClass.cs

@@ -0,0 +1,56 @@
+/* The Knows API is defined in the parent class Relation.
+      bool Knows(int a, int b); */
+
+public class Solution : Relation {
+
+    // TC => O(n)
+    // SC => O(1)
+    public int FindCelebrity(int n){
+        if(n <= 1)
+        {
+            return -1;
+        }
+        int celeb = 0;
+
+       for(int i = 0; i< n; i++){
+        if(i != celeb && Knows(celeb, i)){
+            celeb = i;
+        }
+       }
+
+        for(int k = 0; k < n; k++){
+            if(k != celeb && (!Knows(k, celeb) || Knows(celeb, k))){
+               return -1;
+            }
+        }
+
+        return celeb;
+    }
+
+    // TC => O(n^2)
+    // SC => O(n)
+    public int FindCelebrity1(int n) {
+        if(n <= 1)
+        {
+            return -1;
+        }
+        int[] relations = new int[n];
+
+        for(int i = 0; i< n; i++){
+            for(int j = 0; j < n; j++){
+                if(Knows(i, j)){
+                    relations[i]--;
+                    relations[j]++;
+                }
+            }
+        }
+
+        for(int i = 0; i < n; i++){
+            if(relations[i] == n-1){
+                return i;
+            }
+        }
+
+        return -1;
+    }
+}

MinCostToSupplyWaterClass.cs

@@ -0,0 +1,49 @@
+// TC => O(n+mlog(n+m))
+// SC => O(n+m)
+public class Solution {
+    int[] uf;
+    public int MinCostToSupplyWater(int n, int[] wells, int[][] pipes) {
+        if(n == 0){
+            return 0;
+        }
+        uf = new int[n + 1];
+        for(int i = 0; i< n+1; i++){
+            uf[i] = i;
+        }
+
+        List<int[]> edges = new List<int[]>();
+        for(int i = 0; i< n; i++){
+            edges.Add([0, i+1, wells[i]]);
+        }
+
+        foreach(var pipe in pipes){
+            edges.Add(pipe);
+        }
+
+        edges.Sort(Comparer<int[]>.Create((a,b) => 
+        {
+            return a[2] - b[2];
+        }));
+
+        int total = 0;
+        foreach(var edge in edges){
+            int x = edge[0];
+            int y = edge[1];
+            int cost = edge[2];
+            int px = Find(x);
+            int py = Find(y);
+            if(px != py){
+                total += cost;
+                uf[px] = py;
+            }
+        }
+        return total;
+    }
+    public int Find(int x){
+        if(x != uf[x]){
+            uf[x] = Find(uf[x]);
+        }
+
+        return uf[x];
+    }
+}