Class Solution
Hard
You have a pointer at index 0
in an array of size arrLen
. At each step, you can move 1 position to the left, 1 position to the right in the array, or stay in the same place (The pointer should not be placed outside the array at any time).
Given two integers steps
and arrLen
, return the number of ways such that your pointer still at index 0
after exactly steps
steps. Since the answer may be too large, return it modulo 109 + 7
.
Example 1:
Input: steps = 3, arrLen = 2
Output: 4
Explanation: There are 4 differents ways to stay at index 0 after 3 steps.
Right, Left, Stay
Stay, Right, Left
Right, Stay, Left
Stay, Stay, Stay
Example 2:
Input: steps = 2, arrLen = 4
Output: 2
Explanation: There are 2 differents ways to stay at index 0 after 2 steps
Right, Left
Stay, Stay
Example 3:
Input: steps = 4, arrLen = 2
Output: 8
Constraints:
1 <= steps <= 500
1 <= arrLen <= 106
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Constructor Summary
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Method Summary
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
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Constructor Details
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Solution
public Solution()
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Method Details
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numWays
public int numWays(int steps, int arrLen)
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