problems(cpp): add “881. Boats to Save People”

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

problems/boats-to-save-people.cpp

@@ -0,0 +1,27 @@
+#include <algorithm>
+#include <vector>
+
+class Solution {
+public:
+    int numRescueBoats(std::vector<int> people, int limit)
+    {
+        std::sort(people.begin(), people.end());
+
+        int counter = 0;
+
+        std::size_t left = 0, right = people.size() - 1;
+        while (left <= right && left < people.size() && right < people.size()) {
+            counter++;
+
+            // if they both it, shift the left pointer
+            if (left < right && people[left] + people[right] <= limit) {
+                left++;
+            }
+
+            // anyways, at least the heaviest person is included
+            right--;
+        }
+
+        return counter;
+    }
+};