Test System

Most of my development is done on a Intel® Core™ i7-2600K CPU @ 3.40GHz.
My default compiler is G++ with a x86_64 target and its command-line settings are
g++ -O3 -march=native -fno-exceptions -fno-rtti -std=gnu++11

All solutions are single-threaded and run on the CPU only (no GPU etc.).

You'll find below the following Top Ten lists:

In addition a summary of the difficulty is presented.

Execution Time

The majority of my C++ solutions need much longer to compile than to run.
The "slowest" solutions are (user time displayed by time, single core only):

problem seconds
501 - Eight Divisors 56.33 seconds
407 - Idempotents 46.52 seconds
549 - Divisibility of factorials 26.77 seconds
141 - Investigating progressive numbers, n, which are ... 21.33 seconds
473 - Phigital number base 19.34 seconds
154 - Exploring Pascal's pyramid 16.53 seconds
211 - Divisor Square Sum 14.64 seconds
229 - Four Representations using Squares 10.46 seconds
358 - Cyclic numbers 9.56 seconds
386 - Maximum length of an antichain 8.92 seconds

Note: 185 out of 299 solutions find the correct result in less than 0.1 seconds.

It's not an "officially enforced" limit but each Project Euler problem should be solvable in less than 60 seconds.
I needed much longer to find the correct solutions for a few problems.
Some of them can be heavily parallelized, but the timings below still refer to the slower single-core version:

problem seconds OpenMP support
611 - Hallway of square steps 5692 seconds yes
216 - Investigating the primality of numbers of the form ... 1960 seconds yes
343 - Fractional Sequences 147 seconds yes
291 - Panaitopol Primes 121 seconds yes
411 - Uphill paths 92 seconds yes

Memory Consumption

The GCC standard library consumes about 2 MByte RAM (basic I/O, etc.).
According to Project Euler, the problems are designed such that a smart solution needs no more than 256 MByte.

problem peak memory consumption
411 - Uphill paths 234.6 MByte
259 - Reachable Numbers 138.6 MByte
341 - Golomb's self-describing sequence 133.3 MByte
425 - Prime connection 113.6 MByte
155 - Counting Capacitor Circuits 105.7 MByte
165 - Intersections 68.9 MByte
581 - 47-smooth triangular numbers 67.9 MByte
309 - Integer Ladders 59.2 MByte
358 - Cyclic numbers 47.7 MByte
303 - Multiples with small digits 46.2 MByte

Note: 192 out of 299 solutions allocate less than 2.5 MByte.

Some solutions could be modified to use smaller data types, especially because an int is 8 bytes on my system (64 bit compiler).
The size of the compiled binary is never an issue regarding memory consumption because all are way below 100 kByte (vast majority only about 10 kByte).

It's not an "officially enforced" limit but each Project Euler problem should be solvable with less than 256 MByte memory.
I needed much more to find the correct solution to these problems:

problem peak memory consumption factor
461 - Almost Pi 634 MByte 2.47x

"Expensive" Solutions

These solutions require both lots of CPU time and tons of memory.
I multiply execution time in seconds by memory consumption in MByte to get my "factor".
Solutions with a  colored  background exceed either the CPU or memory limit (or both) and obviously dominate this list.

problem factor
611 - Hallway of square steps 83257.5
411 - Uphill paths 21567.7
216 - Investigating the primality of numbers of the form ... 17364.0
461 - Almost Pi 4257.2
407 - Idempotents 1916.1
549 - Divisibility of factorials 1103.2
501 - Eight Divisors 822.4
343 - Fractional Sequences 480.5
358 - Cyclic numbers 456.1
291 - Panaitopol Primes 277.9

"Lopsided" Solutions

These solutions require lots of CPU time or tons of memory - but not both.
Usually there is a trade-off between CPU time and memory consumption and most likely I didn't find a proper balance for these problems.
My standard approach is to prefer faster code and accept higher memory usage - as long as it's below 256 MByte.

I divide execution time in seconds by memory consumption in MByte to get my "imbalance", if it's smaller than one then I take it's inverse.

problem imbalance seconds peak memory consumption
291 - Panaitopol Primes 3,452 120.81 seconds   2.3 MByte  
341 - Golomb's self-describing sequence 1,139 0.11 seconds   133.3 MByte  
141 - Investigating progressive numbers, n, which are ... 928 21.33 seconds   2.3 MByte  
208 - Numbers for which Euler's totient function equals ... 844 0.03 seconds   31.8 MByte  
113 - Non-bouncy numbers 645 0.02 seconds   18.4 MByte  
611 - Hallway of square steps 460 5691.65 seconds   14.6 MByte  
  72 - Counting fractions 320 0.03 seconds   13.5 MByte  
216 - Investigating the primality of numbers of the form ... 297 1959.82 seconds   8.9 MByte  
571 - Super Pandigital Numbers 287 8.88 seconds   2.3 MByte  
148 - Exploring Pascal's triangle 236 3.53 seconds   2.3 MByte  
Note: to compensate for timing inaccuracies I added 0.005 seconds to each execution time when computing the imbalance.
Moreover, the memory overhead of the C++ runtime is estimated to be 2.26 MByte and subtracted from peak memory usage.

Code Metrics

C++ programs tend to be a bit longer than other popular languages (such as Python).
The metric "lines of code" excludes comments, empty lines and preprocessor commands.

About half of the program in the Top Ten are related to primes numbers. My Miller-Rabin primality test needs about 150 lines.
In general, most of the "bigger" solution contain a substantial amount of code that I just copy from my toolbox.
The actual amount of original code is therefore substantially lower.

problem lines of code comments blank lines
343 - Fractional Sequences 240 86 59
284 - Steady Squares 240 56 56
304 - Primonacci 236 77 63
  80 - Square root digital expansion 234 66 42
152 - Writing 1/2 as a sum of inverse squares 209 74 44
  60 - Prime pair sets 206 65 38
146 - Investigating a Prime Pattern 190 60 42
  54 - Poker hands 188 28 26
126 - Cuboid layers 187 57 40
280 - Ant and seeds 179 56 46

Note: 112 out of 299 solutions have less than 50 lines of code.

Difficulty

Each problem has a "rating" at Project Euler. Very easy ones have a rating of 5%, while the highest is 100%.
The right column shows how many of my solved problems fall into that category.

rating solved problems links
5% 63 21.1% 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 (and 48 more)
10% 9 3.0% 54, 69, 71, 76, 81, 99, 357, 387, 549
15% 18 6.0% 51, 62, 65, 73, 74, 85, 93, 102, 112, 205, 301, 345, 346, 347, 381, 493, 500, 504
20% 20 6.7% 60, 61, 64, 70, 72, 80, 82, 87, 89, 145, 187, 315, 323, 407, 429 (and 5 more)
25% 24 8.0% 66, 68, 75, 77, 83, 91, 96, 104, 120, 124, 125, 179, 203, 293, 329 (and 9 more)
30% 15 5.0% 78, 95, 100, 108, 113, 116, 119, 123, 173, 204, 313, 321, 371, 461, 510
35% 25 8.4% 84, 86, 94, 98, 101, 107, 114, 115, 117, 121, 151, 188, 243, 277, 288 (and 10 more)
40% 17 5.7% 88, 90, 110, 122, 131, 174, 207, 214, 231, 235, 265, 287, 327, 386, 418, 455, 501
45% 24 8.0% 103, 105, 109, 111, 118, 129, 130, 132, 134, 135, 136, 138, 142, 162, 164 (and 9 more)
50% 23 7.7% 106, 127, 133, 137, 139, 144, 146, 148, 149, 166, 169, 190, 211, 215, 230 (and 8 more)
55% 12 4.0% 126, 128, 150, 158, 172, 178, 185, 193, 218, 250, 284, 306
60% 13 4.3% 141, 154, 155, 159, 160, 182, 186, 209, 213, 222, 240, 249, 523
65% 15 5.0% 147, 152, 165, 168, 196, 200, 201, 226, 227, 232, 239, 247, 266, 274, 280
70% 18 6.0% 156, 161, 163, 170, 171, 181, 189, 199, 208, 219, 229, 237, 244, 248, 259, 260, 268, 273
75% - -
80% - -
85% - -
90% - -
95% - -
100% - -
(unknown) 3 1.0% 607, 610, 611
299 32.4%

Heatmap

Please click on a problem's number to open my solution to that problem:

green   solutions solve the original Project Euler problem and have a perfect score of 100% at Hackerrank, too
yellow solutions score less than 100% at Hackerrank (but still solve the original problem easily)
gray problems are already solved but I haven't published my solution yet
blue solutions are relevant for Project Euler only: there wasn't a Hackerrank version of it (at the time I solved it) or it differed too much
orange problems are solved but exceed the time limit of one minute or the memory limit of 256 MByte
red problems are not solved yet but I wrote a simulation to approximate the result or verified at least the given example - usually I sketched a few ideas, too
black problems are solved but access to the solution is blocked for a few days until the next problem is published
  the flashing problem is the one I solved most recently
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The 299 solved problems (that's level 11) had an average difficulty of 32.4% at Project Euler and
I scored 13526 points (out of 15700 possible points, top rank was 17 out of ≈60000 in August 2017) at Hackerrank's Project Euler+.

My username at Project Euler is stephanbrumme while it's stbrumme at Hackerrank.

Look at my progress and performance pages to get more details.

more about me can be found on my homepage, especially in my coding blog.
some names mentioned on this site may be trademarks of their respective owners.
thanks to the KaTeX team for their great typesetting library !