#binary search
#searches for an s in i that satisfies x == f(i[s])
#i = iterable
#f = function to call on each element of i
#x = value to search for
#start = offset into iterable to start
#end = offset into iterable to end
#if it finds a match, it returns a tuple of (s,i[s],f(i[s]))
#if it does not find a match, it returns (-1,None,None)
def bsearch(i,f,x,start=0,end=-1):
if end == -1:
end = len(i)-1
#s = _bsearch(i,f,start,end,x)
s = _bsearch2(i,f,start,end,x)
return (s,i[s],f(i[s])) if s != -1 else (s,None,None)
#recursive
def _bsearch(i,f,lo,hi,x):
if hi >= lo:
md = (hi+lo)//2
a = f(i[md])
if a == x:
return md
elif a > x:
return _bsearch(i,f,lo,md-1,x)
else:
return _bsearch(i,f,md+1,hi,x)
else:
return -1
#loop
def _bsearch2(i,f,lo,hi,x):
while True:
if hi >= lo:
md = (hi+lo)//2
a = f(i[md])
if a == x:
return md
elif a > x:
hi = md-1
else:
lo = md+1
else:
return -1
