cpp: add “2125. Number of Laser Beams in a Bank”

Signed-off-by: Matej Focko <me@mfocko.xyz>

cpp/number-of-laser-beams-in-a-bank.cpp

@@ -0,0 +1,21 @@
+#include <algorithm>
+#include <string>
+#include <vector>
+
+class Solution {
+public:
+    int numberOfBeams(const std::vector<std::string>& bank) {
+        int beams = 0;
+
+        int last_row = 0;
+        for (const auto& row : bank) {
+            if (auto current_row = std::count(row.begin(), row.end(), '1'); current_row != 0) {
+                beams += last_row * current_row;
+                last_row = current_row;
+            }
+        }
+
+        return beams;
+    }
+};
+