problems(rs): add „342. Power of Four“

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/power-of-four.rs

@@ -0,0 +1,15 @@
+impl Solution {
+    pub fn is_power_of_four(n: i32) -> bool {
+        if n == 0 {
+            return false;
+        }
+
+        let mut x = n;
+
+        while x % 4 == 0 {
+            x >>= 2;
+        }
+
+        x == 1
+    }
+}