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/TLE.cpp

@@ -0,0 +1,40 @@
+#include <bits/stdc++.h>
+
+typedef long long ll;
+using namespace std;
+
+int ways(string &s, int n, int idx = 0)
+{
+    if (idx > n)
+        return 1;
+    if (s[idx] == '0')
+        return 0;
+
+    int count = ways(s, n, idx + 1);
+    if (idx + 1 < n)
+    {
+        int num = stoi(s.substr(idx, 2));
+        if (num >= 10 && num <= 26)
+            count += ways(s, n, idx + 2);
+    }
+
+    return count;
+}
+
+vector<bool> used;
+int numDecodings(string &s)
+{
+    int n = (int)s.size();
+    used.resize(n, false);
+    return ways(s, n);
+}
+
+int main()
+{
+    int n;
+    cin >> n;
+    string code;
+    cin >> code;
+    cout << numDecodings(code) << endl;
+    return 0;
+}

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;
+}

decode-ways/src/generator.cpp

@@ -30,6 +30,9 @@ vector<string> generate_sample_tests() {
 vector<string> generate_manual_tests() {
 	vector<string> tests;
 	tests.push_back(output_tc("101010101010"));
+	tests.push_back(output_tc("11111111111111111111"));
+	tests.push_back(output_tc("111111111111111111111111111111111111111111111"));
+	tests.push_back(output_tc("111111111111111111111000000000000000000000000"));
 	tests.push_back(output_tc("123456789"));
 	return tests;
 }