How many Distinct triangle can be made from stick of length N?
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You are given a stick of length N. You want to break it in three pieces such that it can form a triangle. How many distinct triangles can you make? Two triangles are equal if all the side lengths are same when sorted in ascending order of length. So (1, 3, 2) is same to (3, 1, 2) because their side lengths are same if we sort them, which is (1, 2, 3). But (1, 3, 4) is not same with (1, 2, 3). Suppose the lengths of three pieces are X, Y, Z (X ≤ Y ≤ Z) respectively. Following constraints should be maintained:
X, Y, Z > 0.
X, Y, Z is an integer.
X + Y >= Z
X + Y + Z = N
For example if N = 14, then there are 7 triangles: (1, 6, 7), (2, 5, 7), (2, 6, 6), (3, 4, 7), (3, 5, 6), (4, 4, 6), (4, 5, 5).
combinatorics geometry
edited Nov 21 '17 at 14:31
CiaPan
10k11247
asked Jan 3 '16 at 13:31
Code MechanicCode Mechanic
135
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|
show 1 more comment
$begingroup$
You are given a stick of length N. You want to break it in three pieces such that it can form a triangle. How many distinct triangles can you make? Two triangles are equal if all the side lengths are same when sorted in ascending order of length. So (1, 3, 2) is same to (3, 1, 2) because their side lengths are same if we sort them, which is (1, 2, 3). But (1, 3, 4) is not same with (1, 2, 3). Suppose the lengths of three pieces are X, Y, Z (X ≤ Y ≤ Z) respectively. Following constraints should be maintained:
X, Y, Z > 0.
X, Y, Z is an integer.
X + Y >= Z
X + Y + Z = N
For example if N = 14, then there are 7 triangles: (1, 6, 7), (2, 5, 7), (2, 6, 6), (3, 4, 7), (3, 5, 6), (4, 4, 6), (4, 5, 5).
combinatorics geometry
edited Nov 21 '17 at 14:31
CiaPan
10k11247
asked Jan 3 '16 at 13:31
Code MechanicCode Mechanic
135
$endgroup$
$begingroup$
It might help to know that the triangle inequality test can be simplified here to check the sum of two smaller parts exceeds the larger part.
$endgroup$
– hardmath
Jan 3 '16 at 13:37
2
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Hint: The longest side cannot be bigger than $N/2$, and cannot be smaller than $N/3$.
$endgroup$
– Frentos
Jan 3 '16 at 13:37
1
$begingroup$
(1,6,7),(2,5,7), and (3,4,7) will not make triangles.The sum of any two sides must be strictly greater than the third side.
$endgroup$
– DanielWainfleet
Jan 3 '16 at 13:43
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@user254665 , look at the constrains , X + Y >= Z , where on earth you found strictly greater ?
$endgroup$
– Code Mechanic
Jan 3 '16 at 13:44
1
$begingroup$
oeis.org/A005044 gives the sequence for the number of non-degenerate triangles (i.e., not counting those with $X+Y=Z$).
$endgroup$
– Barry Cipra
Jan 3 '16 at 13:56
|
show 1 more comment
$begingroup$
You are given a stick of length N. You want to break it in three pieces such that it can form a triangle. How many distinct triangles can you make? Two triangles are equal if all the side lengths are same when sorted in ascending order of length. So (1, 3, 2) is same to (3, 1, 2) because their side lengths are same if we sort them, which is (1, 2, 3). But (1, 3, 4) is not same with (1, 2, 3). Suppose the lengths of three pieces are X, Y, Z (X ≤ Y ≤ Z) respectively. Following constraints should be maintained:
X, Y, Z > 0.
X, Y, Z is an integer.
X + Y >= Z
X + Y + Z = N
For example if N = 14, then there are 7 triangles: (1, 6, 7), (2, 5, 7), (2, 6, 6), (3, 4, 7), (3, 5, 6), (4, 4, 6), (4, 5, 5).
combinatorics geometry
edited Nov 21 '17 at 14:31
CiaPan
10k11247
asked Jan 3 '16 at 13:31
Code MechanicCode Mechanic
135
$endgroup$
You are given a stick of length N. You want to break it in three pieces such that it can form a triangle. How many distinct triangles can you make? Two triangles are equal if all the side lengths are same when sorted in ascending order of length. So (1, 3, 2) is same to (3, 1, 2) because their side lengths are same if we sort them, which is (1, 2, 3). But (1, 3, 4) is not same with (1, 2, 3). Suppose the lengths of three pieces are X, Y, Z (X ≤ Y ≤ Z) respectively. Following constraints should be maintained:
X, Y, Z > 0.
X, Y, Z is an integer.
X + Y >= Z
X + Y + Z = N
For example if N = 14, then there are 7 triangles: (1, 6, 7), (2, 5, 7), (2, 6, 6), (3, 4, 7), (3, 5, 6), (4, 4, 6), (4, 5, 5).
combinatorics geometry
combinatorics geometry
edited Nov 21 '17 at 14:31
CiaPan
10k11247
asked Jan 3 '16 at 13:31
Code MechanicCode Mechanic
135
edited Nov 21 '17 at 14:31
CiaPan
10k11247
asked Jan 3 '16 at 13:31
Code MechanicCode Mechanic
135
edited Nov 21 '17 at 14:31
CiaPan
10k11247
edited Nov 21 '17 at 14:31
CiaPan
10k11247
edited Nov 21 '17 at 14:31
CiaPan
10k11247
10k11247
asked Jan 3 '16 at 13:31
Code MechanicCode Mechanic
135
asked Jan 3 '16 at 13:31
Code MechanicCode Mechanic
135
asked Jan 3 '16 at 13:31
Code MechanicCode Mechanic
135
135
$begingroup$
It might help to know that the triangle inequality test can be simplified here to check the sum of two smaller parts exceeds the larger part.
$endgroup$
– hardmath
Jan 3 '16 at 13:37
2
$begingroup$
Hint: The longest side cannot be bigger than $N/2$, and cannot be smaller than $N/3$.
$endgroup$
– Frentos
Jan 3 '16 at 13:37
1
$begingroup$
(1,6,7),(2,5,7), and (3,4,7) will not make triangles.The sum of any two sides must be strictly greater than the third side.
$endgroup$
– DanielWainfleet
Jan 3 '16 at 13:43
$begingroup$
@user254665 , look at the constrains , X + Y >= Z , where on earth you found strictly greater ?
$endgroup$
– Code Mechanic
Jan 3 '16 at 13:44
1
$begingroup$
oeis.org/A005044 gives the sequence for the number of non-degenerate triangles (i.e., not counting those with $X+Y=Z$).
$endgroup$
– Barry Cipra
Jan 3 '16 at 13:56
|
show 1 more comment
$begingroup$
It might help to know that the triangle inequality test can be simplified here to check the sum of two smaller parts exceeds the larger part.
$endgroup$
– hardmath
Jan 3 '16 at 13:37
2
$begingroup$
Hint: The longest side cannot be bigger than $N/2$, and cannot be smaller than $N/3$.
$endgroup$
– Frentos
Jan 3 '16 at 13:37
1
$begingroup$
(1,6,7),(2,5,7), and (3,4,7) will not make triangles.The sum of any two sides must be strictly greater than the third side.
$endgroup$
– DanielWainfleet
Jan 3 '16 at 13:43
$begingroup$
@user254665 , look at the constrains , X + Y >= Z , where on earth you found strictly greater ?
$endgroup$
– Code Mechanic
Jan 3 '16 at 13:44
1
$begingroup$
oeis.org/A005044 gives the sequence for the number of non-degenerate triangles (i.e., not counting those with $X+Y=Z$).
$endgroup$
– Barry Cipra
Jan 3 '16 at 13:56
$begingroup$
It might help to know that the triangle inequality test can be simplified here to check the sum of two smaller parts exceeds the larger part.
$endgroup$
– hardmath
Jan 3 '16 at 13:37
$begingroup$
It might help to know that the triangle inequality test can be simplified here to check the sum of two smaller parts exceeds the larger part.
$endgroup$
– hardmath
Jan 3 '16 at 13:37
2
2
$begingroup$
Hint: The longest side cannot be bigger than $N/2$, and cannot be smaller than $N/3$.
$endgroup$
– Frentos
Jan 3 '16 at 13:37
$begingroup$
Hint: The longest side cannot be bigger than $N/2$, and cannot be smaller than $N/3$.
$endgroup$
– Frentos
Jan 3 '16 at 13:37
1
1
$begingroup$
(1,6,7),(2,5,7), and (3,4,7) will not make triangles.The sum of any two sides must be strictly greater than the third side.
$endgroup$
– DanielWainfleet
Jan 3 '16 at 13:43
$begingroup$
(1,6,7),(2,5,7), and (3,4,7) will not make triangles.The sum of any two sides must be strictly greater than the third side.
$endgroup$
– DanielWainfleet
Jan 3 '16 at 13:43
$begingroup$
@user254665 , look at the constrains , X + Y >= Z , where on earth you found strictly greater ?
$endgroup$
– Code Mechanic
Jan 3 '16 at 13:44
$begingroup$
@user254665 , look at the constrains , X + Y >= Z , where on earth you found strictly greater ?
$endgroup$
– Code Mechanic
Jan 3 '16 at 13:44
1
1
$begingroup$
oeis.org/A005044 gives the sequence for the number of non-degenerate triangles (i.e., not counting those with $X+Y=Z$).
$endgroup$
– Barry Cipra
Jan 3 '16 at 13:56
$begingroup$
oeis.org/A005044 gives the sequence for the number of non-degenerate triangles (i.e., not counting those with $X+Y=Z$).
$endgroup$
– Barry Cipra
Jan 3 '16 at 13:56
|
show 1 more comment
1 Answer
1
active
oldest
votes
$begingroup$
As noted by Barry Cipra, the number of nondegenerate triangles is given in OEIS A005044. Allowing degenerate ones (due to the restriction $X+Y ge Z$ permitting equality) adds $lfloor frac n4 rfloor$ when $n$ is even and makes no change when $n$ is odd. This is because to have $X+Y=Z$ with $X le Y le Z$ we must have $Z$ even, then we count the values for $X$ as from $1$ to $lfloor frac Z2 rfloor$ I didn't find the resulting sequence in OEIS.
edited Apr 10 '17 at 23:28
Deepak
17.4k11538
answered Jan 3 '16 at 14:23
Ross MillikanRoss Millikan
299k24200374
$endgroup$
add a comment |
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$begingroup$
As noted by Barry Cipra, the number of nondegenerate triangles is given in OEIS A005044. Allowing degenerate ones (due to the restriction $X+Y ge Z$ permitting equality) adds $lfloor frac n4 rfloor$ when $n$ is even and makes no change when $n$ is odd. This is because to have $X+Y=Z$ with $X le Y le Z$ we must have $Z$ even, then we count the values for $X$ as from $1$ to $lfloor frac Z2 rfloor$ I didn't find the resulting sequence in OEIS.
edited Apr 10 '17 at 23:28
Deepak
17.4k11538
answered Jan 3 '16 at 14:23
Ross MillikanRoss Millikan
299k24200374
$endgroup$
add a comment |
$begingroup$
As noted by Barry Cipra, the number of nondegenerate triangles is given in OEIS A005044. Allowing degenerate ones (due to the restriction $X+Y ge Z$ permitting equality) adds $lfloor frac n4 rfloor$ when $n$ is even and makes no change when $n$ is odd. This is because to have $X+Y=Z$ with $X le Y le Z$ we must have $Z$ even, then we count the values for $X$ as from $1$ to $lfloor frac Z2 rfloor$ I didn't find the resulting sequence in OEIS.
edited Apr 10 '17 at 23:28
Deepak
17.4k11538
answered Jan 3 '16 at 14:23
Ross MillikanRoss Millikan
299k24200374
$endgroup$
add a comment |
$begingroup$
As noted by Barry Cipra, the number of nondegenerate triangles is given in OEIS A005044. Allowing degenerate ones (due to the restriction $X+Y ge Z$ permitting equality) adds $lfloor frac n4 rfloor$ when $n$ is even and makes no change when $n$ is odd. This is because to have $X+Y=Z$ with $X le Y le Z$ we must have $Z$ even, then we count the values for $X$ as from $1$ to $lfloor frac Z2 rfloor$ I didn't find the resulting sequence in OEIS.
edited Apr 10 '17 at 23:28
Deepak
17.4k11538
answered Jan 3 '16 at 14:23
Ross MillikanRoss Millikan
299k24200374
$endgroup$
As noted by Barry Cipra, the number of nondegenerate triangles is given in OEIS A005044. Allowing degenerate ones (due to the restriction $X+Y ge Z$ permitting equality) adds $lfloor frac n4 rfloor$ when $n$ is even and makes no change when $n$ is odd. This is because to have $X+Y=Z$ with $X le Y le Z$ we must have $Z$ even, then we count the values for $X$ as from $1$ to $lfloor frac Z2 rfloor$ I didn't find the resulting sequence in OEIS.
edited Apr 10 '17 at 23:28
Deepak
17.4k11538
answered Jan 3 '16 at 14:23
Ross MillikanRoss Millikan
299k24200374
edited Apr 10 '17 at 23:28
Deepak
17.4k11538
edited Apr 10 '17 at 23:28
Deepak
17.4k11538
edited Apr 10 '17 at 23:28
Deepak
17.4k11538
17.4k11538
answered Jan 3 '16 at 14:23
Ross MillikanRoss Millikan
299k24200374
answered Jan 3 '16 at 14:23
Ross MillikanRoss Millikan
299k24200374
answered Jan 3 '16 at 14:23
Ross MillikanRoss Millikan
299k24200374
299k24200374
add a comment |
add a comment |
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$begingroup$
It might help to know that the triangle inequality test can be simplified here to check the sum of two smaller parts exceeds the larger part.
$endgroup$
– hardmath
Jan 3 '16 at 13:37
2
$begingroup$
Hint: The longest side cannot be bigger than $N/2$, and cannot be smaller than $N/3$.
$endgroup$
– Frentos
Jan 3 '16 at 13:37
1
$begingroup$
(1,6,7),(2,5,7), and (3,4,7) will not make triangles.The sum of any two sides must be strictly greater than the third side.
$endgroup$
– DanielWainfleet
Jan 3 '16 at 13:43
$begingroup$
@user254665 , look at the constrains , X + Y >= Z , where on earth you found strictly greater ?
$endgroup$
– Code Mechanic
Jan 3 '16 at 13:44
1
$begingroup$
oeis.org/A005044 gives the sequence for the number of non-degenerate triangles (i.e., not counting those with $X+Y=Z$).
$endgroup$
– Barry Cipra
Jan 3 '16 at 13:56