Project Euler/112

From charlesreid1

Problem Statement

ProjectEuler112.png

Analysis

This problem asks for the least positive integer Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle N} such that the proportion of "bouncy" numbers up to Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle N} is exactly 99%.

A number is bouncy if it is neither increasing (digits non-decreasing left-to-right, e.g., 13448) nor decreasing (digits non-increasing left-to-right, e.g., 99740).

Let Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle B(N)} be the count of bouncy numbers Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle \le N} , and Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle NB(N)} be the count of non-bouncy numbers Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle \le N} .

The condition is Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle \frac{B(N)}{N} = 0.99} .

Since Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle B(N) = N - NB(N)} , the condition becomes:

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle \frac{N - NB(N)}{N} = 0.99 \implies 1 - \frac{NB(N)}{N} = 0.99 \implies \frac{NB(N)}{N} = 0.01 }

This means we seek the smallest Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle N} such that Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle NB(N) = \frac{N}{100}} .

A key consequence is that Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle N} must be a multiple of 100.

Non-bouncy numbers are either increasing or decreasing.

Let Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle I(N)} be the count of increasing numbers Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle \le N} and Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle D(N)} be the count of decreasing numbers Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle \le N} .

Numbers with all identical digits (e.g., 555) are both increasing and decreasing; let their count be Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle F(N)} .

By inclusion-exclusion:

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle NB(N) = I(N) + D(N) - F(N) }

While calculating Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle I(N), D(N), F(N)} for arbitrary Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle N} typically requires Digit Dynamic Programming, analytical formulas exist for Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle N=10^k-1} :

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle |I(10^k-1)| = \binom{k+9}{9} - 1}

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle |D(10^k-1)| = \binom{k+10}{10} - 1 - k}

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle |F(10^k-1)| = 9k}

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle |NB(10^k-1)| = \binom{k+9}{9} + \binom{k+10}{10} - 10k - 2}

These formulas show that the proportion of non-bouncy numbers drops below 1.3% for Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle k=6} (Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle N=999,999} ) and below 0.4% for Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle k=7} (Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle N=9,999,999} ), indicating Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle N} is likely greater than Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle 10^6} .

The computational strategy is:

1. Implement functions (likely using Digit DP) to compute Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle NB(N)} accurately for any Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle N} .

2. Search for the target Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle N} by checking multiples of 100, starting from an estimated lower bound (e.g., Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle N \approx 100 \times NB(10^6-1) \approx 1.3 \times 10^6} ).

3. The first Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle N} found such that Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle NB(N) = N/100} is the solution.

Solution

Link to solution: https://git.charlesreid1.com/cs/euler/src/branch/master/java/Problem112.java

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Project Euler

Grid 0: Problems 1-99

Problem 1  · Problem 2  · Problem 3  · Problem 4  · Problem 5  · Problem 6  · Problem 7  · Problem 8  · Problem 9  · Problem 10

Problem 11  · Problem 12  · Problem 13  · Problem 14  · Problem 15  · Problem 16  · Problem 17  · Problem 18  · Problem 19  · Problem 20

Problem 21  · Problem 22  · Problem 23  · Problem 24  · Problem 25  · Problem 26  · Problem 27  · Problem 28  · Problem 29  · Problem 30

Problem 31  · Problem 32  · Problem 33  · Problem 34  · Problem 35  · Problem 36  · Problem 37  · Problem 38  · Problem 39  · Problem 40

Problem 41  · Problem 42  · Problem 43  · Problem 44  · Problem 45  · Problem 46  · Problem 47  · Problem 48  · Problem 49  · Problem 50

Problem 51  · Problem 52  · Problem 53  · Problem 54  · Problem 55  · Problem 56  · Problem 57  · Problem 58  · Problem 59  · Problem 60

Problem 61  · Problem 62  · Problem 63  · Problem 64  · Problem 65  · Problem 66  · Problem 67  · Problem 68  · Problem 69  · Problem 70

Problem 71  · Problem 72  · Problem 73  · Problem 74  · Problem 75  · Problem 76  · Problem 77  · Problem 78  · Problem 79  · Problem 80

Grid 1: Problems 100-199

Problem 100  · Problem 101  · Problem 102  · Problem 103  · Problem 104  · Problem 105  · Problem 106  · Problem 107  · Problem 108  · Problem 109

...

Problem 150  · Problem 151  · Problem 152  · Problem 153  · Problem 154  · Problem 155  · Problem 156  · Problem 157  · Problem 158  · Problem 159

...

Problem 170  · Problem 171  · Problem 172  · Problem 173  · Problem 174  · Problem 175  · Problem 176  · Problem 177  · Problem 178  · Problem 179

...


Problem 190  · Problem 191  · Problem 192  · Problem 193  · Problem 194  · Problem 195  · Problem 196  · Problem 197  · Problem 198  · Problem 199


Grid 2: Problems 200-299

Problem 227  · Problem 254


Grid 3: Problems 300-399


Problem 301  · Problem 310

Problem 312  · Problem 319

Problem 323  · Problem 328

Problem 334  · Problem 337

Problem 345  · Problem 346

Problem 355  · Problem 356

Problem 364  · Problem 367

Problem 373  · Problem 378

Problem 382  · Problem 389

Problem 391

Grid 5: Problems 500-599

Problem 400


Grid 5: Problems 500-599

Problem 500  · Problem 501  · Problem 502


Grid 9: Problems 900-999

Problem 932


* = in progress

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