Finding longest consecutive numbers in array

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John Doe
John Doe 2018-1-27
评论： Martina 2025-10-24，15:10
Hello everyone,
This is somewhat of a silly question but I can't seem to figure it out. If I have an array of numbers what I want is to find the location of my longest consecutive numbers for example:
my arrary = [ 1999 2000 2001 2003 2004 2005 2006 2007];
I want my output to be = [ 4 5 6 7 8]; because that's the location of my longest consecutive numbers (2003-2007). I tried to find where difference is equal to 1 but then the result is [1 1 1 0 1 1 1 1] , it doesn't take the position of the last number which is 2007 here and even if I fix that problem also I'd still have to find the locations for the longest consecutive one's for the second scenario.
I could use some help in this,
Thank You!!!

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Stephen23
Stephen23 2018-1-27
编辑：Stephen23 2025-10-24，14:45
Ran in:
V = [1999,2000,2001,2003,2004,2005,2006,2007];
D = diff([0;diff(V(:))==1;0]);
B = find(D>0);
E = find(D<0);
[~,idx] = max(E-B);
idy = B(idx):E(idx)
idy = 1×5
4 5 6 7 8
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Stephen23
Stephen23 2025-10-24，14:44
编辑：Stephen23 2025-10-24，14:49
Ran in:
@Martina: well spotted! I made a few changes, please check it!
longestConsecutive([2001,2002,2003,2004,2005,2006,2007,2009,2010]) % 1:7
ans = 1×7
1 2 3 4 5 6 7
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longestConsecutive([1999,2001,2003,2004,2005,2006,2007,2009,2010]) % 3:7
ans = 1×5
3 4 5 6 7
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longestConsecutive([1999,2001,2003,2004,2005,2006,2007,2008,2009]) % 3:9
ans = 1×7
3 4 5 6 7 8 9
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longestConsecutive([2001,2002,2003,2004,2005,2006,2007,2008,2009]) % 1:9
ans = 1×9
1 2 3 4 5 6 7 8 9
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longestConsecutive([2001,2003,2005,2007]) % none
ans = 1×0 empty double row vector
function idy = longestConsecutive(inp)
D = diff([0;diff(inp(:))==1;0]);
B = find(D>0);
E = find(D<0);
[~,idx] = max(E-B);
idy = B(idx):E(idx);
end
As an alternative you could use something from FEX, for example
https://www.mathworks.com/matlabcentral/fileexchange/41813-runlength
on the DIFF() of the vector.

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