cpp: add “907. Sum of Subarray Minimums”

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

cpp/sum-of-subarray-minimums.cpp

@@ -0,0 +1,31 @@
+#include <vector>
+
+class Solution {
+    static const int MOD = 1000000007;
+
+  public:
+    int sumSubarrayMins(const std::vector<int> &arr) {
+        long s = 0;
+
+        std::vector<int> stack;
+        for (auto i = 0; i <= static_cast<int>(arr.size()); ++i) {
+            while (!stack.empty() &&
+                   (i == arr.size() || arr[stack.back()] >= arr[i])) {
+                int mid = stack.back();
+                stack.pop_back();
+
+                int l = stack.empty() ? -1 : stack.back();
+                int r = i;
+
+                long count = (mid - l) * (r - mid) % MOD;
+
+                s += (count * arr[mid]) % MOD;
+                s %= MOD;
+            }
+
+            stack.push_back(i);
+        }
+
+        return static_cast<int>(s);
+    }
+};