Create distinct-subsequences-ii.cpp

Author: kamyu104

C++/distinct-subsequences-ii.cpp

@@ -0,0 +1,17 @@
+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    int distinctSubseqII(string S) {
+        static const int M = 1e9 + 7;
+        vector<int> dp(26);
+        int result = 0;  // sum of dp
+        for (const auto& c : S) {
+            tie(result, dp[c - 'a']) =
+                make_pair(((2 * result) % M - dp[c - 'a'] + 1) % M,
+                          (result + 1) % M);
+        }
+        return (result + M) % M;
+    }
+};