PE 76, took a while to notice you need to subtract 1 from the partition function

projecteuler/076/main.cpp

@@ -0,0 +1,44 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int MAX_N = 100;
+
+vector<unsigned long long> partition_function(MAX_N + 1, -1);
+
+int partitioning(int n){
+    unsigned long long result = 0;
+
+    for(int k = 1; k <= n; ++k){
+        int lower = n - k*(3 * k - 1) / 2;
+        int upper = n - k*(3 * k + 1) / 2;
+        result += (k % 2 == 0 ? -1 : 1) * ((upper >= 0 ? partition_function[upper] : 0) + (lower >=0 ? partition_function[lower] : 0));
+    }
+
+    return result;
+}
+
+int main(){
+
+    cout << "Hello this is Patrick" << endl;
+    auto start = chrono::high_resolution_clock::now();
+
+    // Use partition theory: https://en.wikipedia.org/wiki/Partition_(number_theory)
+    // https://kylekizirian.github.io/euler-partition-function.html
+
+    partition_function[0] = 1;
+
+    for(int n = 1; n <= MAX_N; ++n){
+        partition_function[n] = partitioning(n);
+    }
+
+    // for(unsigned long long i : partition_function){
+    //     cout << i << " ";
+    // } cout << endl;
+
+    cout << partition_function[MAX_N] - 1 << endl;
+
+    auto duration = chrono::duration_cast<chrono::milliseconds>(chrono::high_resolution_clock::now() - start);
+    cout << (float)duration.count()/1000 << endl;
+    return 0;
+}