Solution: Decode Ways

Author: obzva

decode-ways/flynn.cpp

@@ -0,0 +1,29 @@
+/**
+ * For the length of the given string N,
+ * 
+ * Time complexity: O(N)
+ * 
+ * Space complexity: O(N)
+ */
+
+class Solution {
+public:
+    int numDecodings(string s) {
+        if (s[0] == '0') return 0;
+
+        int memo[s.size() + 1];
+
+        fill(memo, memo + s.size() + 1, 0);
+        memo[0] = 1;
+        memo[1] = 1;
+
+        for (int i = 2; i <= s.size(); i++) {
+            int s_i = i - 1;
+            if (s[s_i] != '0') memo[i] = memo[i - 1];
+            int two_digits = stoi(s.substr(s_i - 1, 2));
+            if (10 <= two_digits && two_digits <= 26) memo[i] += memo[i - 2];
+        } 
+
+        return memo[s.size()];
+    }
+};