problems: add number of matching subsequences

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

problems/number-of-matching-subsequences.cpp

@@ -0,0 +1,34 @@
+class Solution {
+    bool matches(const string& s, const string& word) const
+    {
+        auto s_i = 0;
+
+        for (auto i = 0; s_i < s.size() && i < word.size(); i++) {
+            if (s[s_i] == word[i]) {
+                s_i++;
+            }
+        }
+
+        return s_i == s.size();
+    }
+
+    map<string, int> preprocess(const vector<string>& words) const
+    {
+        map<string, int> histogram;
+
+        for (auto& w : words) {
+            histogram[w]++;
+        }
+
+        return histogram;
+    }
+
+public:
+    int numMatchingSubseq(string s, vector<string>& words)
+    {
+        auto histogram = preprocess(words);
+        return accumulate(histogram.begin(), histogram.end(), 0, [&](int acc, const auto& pair) {
+            return acc + (matches(pair.first, s) ? pair.second : 0);
+        });
+    }
+};