Solution of first problem

FixMultiplication.cs

@@ -0,0 +1,67 @@
+using System;
+ public class FixMultiplication
+ {
+
+    public static int isMissing(int t,int T)
+    {
+           int count=0;
+   int missing_digit = -1;
+   int[] ht = new int[10];
+   while(t!=0)
+   {
+	ht[t%10]++;
+	t/=10;
+   }
+   while(T!=0)
+   {
+	ht[T%10]--;
+	T/=10;
+   }
+   for(int i=0;i<=9;i++)
+   {
+	 if(ht[i]==1)
+	 {
+		  count++;
+		  missing_digit = i;
+	 }
+   }
+   if(count!=1)
+	   missing_digit = -1;
+   return missing_digit;
+    }
+       int FindDigit(string inp)
+     {
+         int t=0;
+         string[] inp1 = inp.Split('=');
+         string[] inp2 = inp1[0].Split('*');
+         int A = Convert.ToInt32(inp2[0]);
+         int B = Convert.ToInt32(inp2[1]);
+         int C = Convert.ToInt32(inp1[1]);
+
+         if(A*B<C)
+	 {
+		int a = C/B;
+		int b = C/A;
+		if((t=isMissing(a,A))!=-1)
+		{
+		  return t;
+		}
+		if((t=isMissing(b,B))!=-1)
+		{
+		return t;
+		}
+	 return -1;
+	 }
+	 if(A*B>C)
+	 {
+		return  isMissing(A*B,C);
+	 }
+	 return -1;
+     }
+     public static void Main(String[] args)
+     {
+    string inp = Console.ReadLine();
+    FixMultiplication obj = new FixMultiplication();
+    Console.WriteLine(" "+obj.FindDigit(inp));
+     }
+ }