JavaSolve: Array Is Valley
Write a function isValley that takes an IntArray? and returns true
if and only if it is a valley. An array is a valley if it consists of a single run
of decreasing numbers joined with a single run of increasing numbers.
For example {1, 0, 1} is a valley, since it has the decreasing run {1, 0}
joined with the increasing run {0, 1}.
The runs need not be strictly increasing or strictly decreasing. For example,
{1, 1, 0, 0, 1, 1} is a valley, since it consists of {1, 1, 0, 0} joined with
{0, 0, 1, 1}. However, there must be at least one increase and one decrease
in the array for it to qualify. {1, 1, 0}, {0, 1, 1}, and
{1, 1, 1} should all fail under this condition.
Notice that these conditions require arrays of at least length 3. If your array
is shorter than this or null, return false.
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