feat: added alternative solution and TLE solution to decode-ways problem, wrote the tutorial file and added some more manual test cases

decode-ways/src/alternative_ac.cpp

@@ -0,0 +1,45 @@
+#include <bits/stdc++.h>
+
+typedef long long ll;
+using namespace std;
+
+ll numDecodings(string s)
+{
+    if (s[0] == '0')
+        return 0;
+
+    int N = s.size();
+    ll dp1 = 1, dp2 = 1;
+    for (int i = 2; i <= N; i++)
+    {
+        ll next = 0;
+        char current = s[i - 1], last = s[i - 2];
+        string aux = "";
+        aux += last;
+        aux += current;
+        if (current != '0')
+        {
+            next = dp2;
+        }
+
+        int code = stoi(aux);
+        if (10 <= code && code <= 26)
+        {
+            next += dp1;
+        }
+        swap(dp1, dp2);
+        swap(dp2, next);
+    }
+
+    return dp2;
+}
+
+int main()
+{
+    int n;
+    cin >> n;
+    string code;
+    cin >> code;
+    cout << numDecodings(code) << endl;
+    return 0;
+}