added matrix rotation algorithm

HelloWorld/helloworld.cpp

@@ -1,8 +1,8 @@
-#include<stdio.h>
-#include<iostream>
-
-int main()
-{
-	printf("Hello World!");
-}
-
+#include<stdio.h>
+#include<iostream>
+
+int main()
+{
+	printf("Hello World!");
+}
+

algorithms/Rotate_matrixby90deg.cpp

@@ -0,0 +1,27 @@
+//Rotate matrix by 90 degree
+#include<bits/stdc++.h>
+using namespace std;
+int main()
+{
+    int n;
+    cin>>n;
+    int i,j,matrix[n][n];
+    for(int i=0;i<n;i++)
+        for(int j=0l;j<n;j++)
+            cin>>matrix[i][j];
+        for(i=0;i<n;i++)
+            for(j=i+1;j<n;j++)
+                swap(matrix[i][j],matrix[j][i]);
+        int k;
+        for(k=0;k<n;k++)
+        {
+            i=0,j=n-1;
+            while(j>i)
+            {
+                swap(matrix[k][i],matrix[k][j]);
+                i++;
+                j--;
+            }
+        }
+    return 0;
+}