Project Euler
Posted dgklr
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Solutions to Project Euler
Written by dgklr, often by using python / c++
P125
Answer: 2906969179
Running Time: 1068ms
/* Copyright (c) dgklr */
#include<bits/stdc++.h>
using namespace std;
long long n;
long long li[11000];
long long pre[11000];
bool has[110000000];
const int N = 100000000;
long long ans = 0;
void check(long long ret)
if (ret > N) return;
char c[11];
if (has[ret] == 1) return;
sprintf(c,"%lld",ret);
int len = strlen(c);
for (int i=0;i<len;i++)
if (c[i] != c[len-i-1]) return;
has[ret] = 1;
ans += ret;
int main()
for (int i=1;i*i<=N;i++)
li[i] = i * i, pre[i] = pre[i-1] + li[i];
for (int i=2;i*i<=N;i++)
for (int j=0;j<=i-2;j++)
check(pre[i] - pre[j]);
cout << ans << endl;
P124
Answer: 21417
Running Time: 521ms
/* Copyright (c) dgklr */
#include<bits/stdc++.h>
using namespace std;
#define N 100000
int pl = 0;
int prime[N];
int trans(int x)
int ret = 1;
for (int i=1;i<=pl;i++)
if (x % prime[i] == 0) ret *= prime[i];
while (x % prime[i] == 0) x /= prime[i];
if (x == 1) break;
return ret;
int getprime()
for (int i=2;i<=N;i++)
int flag = 0;
for (int j=2;j*j<=i;j++)
if (i % j == 0) flag = 1; break;
if (!flag) prime[++pl] = i;
pair <int,int> ans[N+2];
int main()
getprime();
for (int i=1;i<=N;i++)
ans[i].first = trans(i);
ans[i].second = i;
sort(ans+1,ans+N+1);
cout << ans[10000].second;
P126
Answer: 18522
Running Time: 81ms
/* Copyright (c) dgklr */
#include<bits/stdc++.h>
#define DEBUG cerr << "Call out: " << __func__ << "\t" << "Line: " << __LINE__ << "\t :"
using namespace std;
const int N = 30000;
int C[N + 4];
int Cubes(int x, int y, int z, int n)
return 2 * (x * y + y * z + x * z ) + 4 * (x + y + z + n - 2) * (n - 1);
int main()
clock_t beg = clock();
for (int i=1;Cubes(i,i,i,1) <= N;i++)
for (int j=i;Cubes(i,j,i,1) <= N;j++)
for (int k=j;Cubes(i,j,k,1) <= N;k++)
for (int l=1;Cubes(i,j,k,l) <= N;l++)
C[Cubes(i,j,k,l)] ++;
for (int i=1;i<=N;i++)
if (C[i] == 1000) cout << i << ' ' << clock()-beg << endl, exit(0);
P123
Answer: 21035
Running Time: 740ms
/* Copyright (c) dgklr */
#include<bits/stdc++.h>
#define DEBUG cerr << "Call out: " << __func__ << "\t" << "Line: " << __LINE__ << "\t :"
using namespace std;
#define MAXN 10000000000ll
long long prime[1000000];
int pl = 0;
#define ll long long
inline ll ksc(ll x,ll y,ll p)
ll res=0;
while(y)
if(y&1)res=(res+x)%p;
x=(x<<1)%p; y>>=1;
return res;
long long ksm(long long x,long long base, long long MOD)
long long ret = 1;
long long xt = x;
while (base > 0)
if (base % 2 == 1) ret = ksc(ret,xt,MOD);
xt = ksc(xt,xt,MOD);
base /= 2;
return ret;
void getprime()
for (int i=2;i<=1000000;i++)
int flag = 0;
for (int j=2;j*j<=i;j++)
if (i%j == 0) flag = 1; break;
if (!flag) prime[++pl] = i;
int main()
clock_t beg = clock();
getprime();
for (int i=1;i;i++)
if ((ksm(prime[i]-1,i,prime[i]*prime[i]) + ksm(prime[i]+1,i,prime[i]*prime[i]))%(prime[i]*prime[i]) > MAXN)
cout << i << ' ' << clock() - beg << "ms"<< endl, exit(0);
P122
Answer: 1582
Running Time:1544ms
/* Copyright (c) dgklr */
#include<bits/stdc++.h>
using namespace std;
const int MAXK = 200;
int opt[20] = 0,1;
int anslist[210] = 0,1;
void dfs(int now,int x)
if (x > 12) return;
if (now > MAXK) return;
if (anslist[now] > x) anslist[now] = x;
opt[x] = now;
for (int i=1;i<=x;i++)
dfs(now+opt[i],x+1);
int main()
int beg = clock();
int ans = 0;
memset(anslist,0x3f,sizeof anslist);
anslist[1] = 1;
dfs(2,2);
for (int i=1;i<=MAXK;i++)
ans += anslist[i]-1;
cout << ans << ' ' <<clock() - beg << "ms" << endl;
P121
ans: 2269
Running Time: 0ms
/* Copyright (c) dgklr */
#include<bits/stdc++.h>
using namespace std;
double f(int n, int i, int r, int b)
if (i == n) return b > r ? 1 : 0;
return 1 * f(n, i + 1, r, b + 1) / (i + 2) + (i + 1) * f(n, i + 1, r + 1, b) / (i + 2);
int main()
int beg = clock();
cout << (int)(1 / f(15, 0, 0, 0)) << endl;
cout << clock() - beg << "ms" << endl;
return 0;
P127
Answer: 18407904
A Better Solution
Running Time: 257ms
#include<bits/stdc++.h>
#define DEBUG cerr << "Call out: " << __func__ << "\t" << "Line: " << __LINE__ << "\t :"
using namespace std;
#define MAXN 120000
int rad[120000];
int prime[120000];
int tot[120000];
int pl;
void getprime()
for (int i=2;i<=MAXN;i++)
int flag = 0;
for (int j=2;j*j<=i;j++)
if (i%j == 0) flag = 1; break;
if (!flag) prime[++pl] = i;
int init()
for (int i=1;i<=MAXN;i++)
int tmp = i;
rad[i] = 1;
for (int j=1;j<=pl;j++)
if (tmp % prime[j] == 0)
rad[i] *= prime[j];
while (tmp % prime[j] == 0) tmp /= prime[j];
if (tmp == 1) break;
if (prime[j] * prime[j] > tmp)
rad[i] *= tmp;
break;
for (int i=1;i<=MAXN;i++)
tot[rad[i]] ++;
long long ans = 0;
set <pair<int,int> > p;
int process(int x,int has)
int ret = 0;
for (auto i : p)
if (i.first * i.first > x) return ret;
if (__gcd(i.second,x) == 1 && __gcd(i.second,has-i.second) == 1 && i.first < rad[has-i.second])
if (i.first * rad[has-i.second] < x) ret += has;
return ret;
int main()
clock_t beg = clock();
getprime();
init();
p.insert(make_pair(1,1));
for (int i=2;i<MAXN;i++)
ans += process(i/rad[i],i);
p.insert(make_pair(rad[i],i));
cout << ans << ' ';
cout << clock() - beg << endl;
Running time: 1111ms
#include<bits/stdc++.h>
#define DEBUG cerr << "Call out: " << __func__ << "\t" << "Line: " << __LINE__ << "\t :"
using namespace std;
#define MAXN 120000
int rad[120000];
int prime[120000];
int tot[120000];
int pl;
void getprime()
for (int i=2;i<=MAXN;i++)
int flag = 0;
for (int j=2;j*j<=i;j++)
if (i%j == 0) flag = 1; break;
if (!flag) prime[++pl] = i;
int init()
for (int i=1;i<=MAXN;i++)
int tmp = i;
rad[i] = 1;
for (int j=1;j<=pl;j++)
if (tmp % prime[j] == 0)
rad[i] *= prime[j];
while (tmp % prime[j] == 0) tmp /= prime[j];
if (tmp == 1) break;
if (prime[j] * prime[j] > tmp)
rad[i] *= tmp;
break;
for (int i=1;i<=MAXN;i++)
tot[rad[i]] ++;
long long ans = 0;
set <pair<int,int> > p;
int process(int x,int has)
map <int,int> h;
int ret = 0;
for (auto i : p)
h[i.second] = 1;
if (i.first * i.first > x) return ret;
if (__gcd(i.second,x) == 1 && __gcd(i.second,has-i.second) == 1 && h[has-i.second] == 0)
if (i.first * rad[has-i.second] < x) ret += has;
return ret;
int main()
clock_t beg = clock();
getprime();
init();
p.insert(make_pair(1,1));
for (int i=2;i<MAXN;i++)
ans += process(i/rad[i],i);
p.insert(make_pair(rad[i],i));
cout << ans << ' ';
cout << clock() - beg << endl;
P128
Answer: 14516824220
Running Time: 201ms
/* Copyright (c) dgklr */
#include<bits/stdc++.h>
using namespace std;
#define int long long
bool IsPrime(int x)
for (int i=2;i * i <=x;i++)
if (x % i == 0) return 0;
return 1;
signed main()
int beg = clock();
int count = 1;
int limit = 2000;
int n = 0;
int number = 0;
while (count < limit)
n++;
if (IsPrime(6 * n - 1) && IsPrime(6 * n + 1) && IsPrime(12 * n + 5))
count++;
number = (3 * n * n - 3*n + 2);
if (count >= limit) break;
if (IsPrime(6 * n + 5) && IsPrime(6 * n - 1) && IsPrime(12 * n - 7) && n != 1)
count++;
number = (3 * n * n + 3*n + 1);
cout << number << ' ' << clock() - beg << "ms" << endl;
return 0;
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