g1201_1300.s1269_number_of_ways_to_stay_in_the_same_place_after_some_steps

Class Solution

java.lang.Object

g1201_1300.s1269_number_of_ways_to_stay_in_the_same_place_after_some_steps.Solution

public class Solution
extends Object

1269 - Number of Ways to Stay in the Same Place After Some Steps.

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

Constructor Summary

Constructors

Constructor and Description
Solution()

Method Summary

Modifier and Type	Method and Description
int	numWays(int steps, int arrLen)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Solution

public Solution()

Method Detail

numWays

public int numWays(int steps,
                   int arrLen)