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Let's say I have an array a of length n and a second array indices, also of length n. indices contains some arbitrary permutation of the sequence [0, n). I want to to rearrange a such that it's in the order specified by indices. For example, using D syntax:
auto a = [8, 6, 7, 5, 3, 0, 9]; auto indices = [3, 6, 2, 4, 0, 1, 5]; reindexInPlace(a, indices); assert(a == [5, 9, 7, 3, 8, 6, 0]); Can this be done in both O(1) space and O(n) time, preferably without mutating indices?
959
Approach used in the below program is as followsDeclare a variable as max_val and set it with arr[size - 1] + 1. Start loop FOR from i to 0 till i less than size. Inside the loop, check IF i % 2 = 0 then set arr[i] to arr[i] + (arr[max] % max_val) * max_val and decrement the max by 1.
It can never be assigned to. When used as a value it is automatically converted to a pointer to the first element, through which the array elements can be accessed and modified.
With mutating indices :(. Without looks hard (see stable in-place mergesort).
a = [8, 6, 7, 5, 3, 0, 9] indices = [3, 6, 2, 4, 0, 1, 5] for i in xrange(len(a)): x = a[i] j = i while True: k = indices[j] indices[j] = j if k == i: break a[j] = a[k] j = k a[j] = x print a If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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