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+/*
+TASK #2 › Unique Sub-sequence
+Submitted by : Mohammad S Anwar
+You are given two strings $S and $T.
+
+Write a script to find out count of different unique sub-sequences matching
+$T without changing the position of characters.
+
+Example 1:
+Input : $S = "littleit', $T = 'lit'
+Output : 5
+
+    1: [lit] tleit
+    2: [li] t[t] leit
+    3: [li] ttlei[t]
+    4: litt[l] e[it]
+    5: [l] ittle[it]
+Example 2:
+Input : $S = "london', $T = 'lon'
+Output : 3
+
+    1: [lon] don
+    2: [lo] ndo[n]
+    3: [l] ond[on]
+*/
+
+#include <iostream>
+
+int count_subsequences(const char* s, const char* t) {
+    while (true) {
+        if (!*t)                // t is empty, matched
+            return 1;
+        else if (!*s)           // s is empty, did not match
+            return 0;
+        else if (*s == *t) {    // same char, check two paths matching and not matching
+            int matching = count_subsequences(s + 1, t + 1);
+            int not_matching = count_subsequences(s + 1, t);
+            return matching + not_matching;
+        }
+        else                    // different char, keep pattern
+            s++;
+    }
+}
+
+int main(int argc, char* argv[]) {
+    if (argc == 3)
+        std::cout << count_subsequences(argv[1], argv[2]) << std::endl;
+    else {
+        std::cerr << "Usage: ch-2 string test" << std::endl;
+        return EXIT_FAILURE;
+    }
+}