feat: add maximum.rs

DIRECTORY.md

@@ -10,6 +10,7 @@
     * [Sudoku](https://github.com/TheAlgorithms/Rust/blob/master/src/backtracking/sudoku.rs)
   * Big Integer
     * [Fast Factorial](https://github.com/TheAlgorithms/Rust/blob/master/src/big_integer/fast_factorial.rs)
+    * [Maximum](https://github.com/TheAlgorithms/Rust/blob/master/src/big_integer/maximum.rs)
     * [Multiply](https://github.com/TheAlgorithms/Rust/blob/master/src/big_integer/multiply.rs)
     * [Poly1305](https://github.com/TheAlgorithms/Rust/blob/master/src/big_integer/poly1305.rs)
   * Bit Manipulation

src/big_integer/maximum.rs

@@ -0,0 +1,33 @@
+/// Compute the multiplication set of the three largest numbers in an array
+pub fn maximum(mut nums: Vec<i32>) -> i32 {
+    nums.sort();
+    (nums[nums.len() - 1] * nums[nums.len() - 2] * nums[nums.len() - 3])
+        .max(nums[0] * nums[nums.len() - 1] * nums[nums.len() - 2])
+        .max(nums[0] * nums[1] * nums[nums.len() - 1])
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    macro_rules! test_maximum {
+        ($($name:ident: $inputs:expr,)*) => {
+        $(
+            #[test]
+            fn $name() {
+                let (s, expected) = $inputs;
+                assert_eq!(maximum(s.to_vec()), expected);
+            }
+        )*
+        }
+    }
+
+    test_maximum! {
+        positive0: ([1,2,3], 6),
+        positive1: ([1,2,3,4], 24),
+        negative0: ([-1,-2,-3], -6),
+        negative1: ([-1,-2,-3,-4,-5], -6),
+        positive_and_negative0: ([-1,-2,-3,4,5], 30),
+        positive_and_negative1: ([-1,2,-3,-4,5], 60),
+        positive_and_negative2: ([-1,2,-3,4,5], 40),
+    }
+}

src/big_integer/mod.rs

@@ -1,9 +1,11 @@
 #![cfg(feature = "big-math")]
 
 mod fast_factorial;
+mod maximum;
 mod multiply;
 mod poly1305;
 
 pub use self::fast_factorial::fast_factorial;
+pub use self::maximum::maximum;
 pub use self::multiply::multiply;
 pub use self::poly1305::Poly1305;