rs: add «930. Binary Subarrays With Sum»

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

rs/binary-subarrays-with-sum.rs

@@ -0,0 +1,34 @@
+impl Solution {
+    pub fn num_subarrays_with_sum(nums: Vec<i32>, goal: i32) -> i32 {
+        let mut subarrays = 0;
+
+        let mut sum = 0;
+        let mut zeros = 0;
+
+        let mut l = 0;
+        for r in 0..nums.len() {
+            sum += nums[r];
+
+            while l < r && (nums[l] == 0 || sum > goal) {
+                match nums[l] {
+                    0 => {
+                        zeros += 1;
+                    }
+                    1 => {
+                        zeros = 0;
+                    }
+                    _ => unreachable!("either 0 or 1s"),
+                }
+
+                sum -= nums[l];
+                l += 1;
+            }
+
+            if sum == goal {
+                subarrays += 1 + zeros;
+            }
+        }
+
+        subarrays
+    }
+}