Move all solutions into separate directory (cleanup)

the beginning

solutions/product-of-array-except-self/src/main.rs

@@ -0,0 +1,33 @@
+struct Solution {}
+
+impl Solution {
+    pub fn product_except_self(nums: Vec<i32>) -> Vec<i32> {
+        let mut result = vec![1; nums.len()];
+        let mut left = 1;
+        let mut right = 1;
+
+        for i in 0..nums.len() {
+            // Moving left to right: multiple each number by the preceding number
+            result[i] *= left;
+            left *= nums[i];
+            
+            // Moving right to left, multiple each number by the following number
+            result[nums.len() - 1 - i] *= right;
+            right *= nums[nums.len() - 1 - i];
+        }
+
+        result
+    }
+}
+
+fn main() {
+    assert_eq!(
+        Solution::product_except_self(vec![1, 2, 3, 4]),
+        vec![24, 12, 8, 6]
+    );
+
+    assert_eq!(
+        Solution::product_except_self(vec![-1, 1, 0, -3, 3]),
+        vec![0, 0, 9, 0, 0]
+    )
+}