g2301_2400.s2400_number_of_ways_to_reach_a_position_after_exactly_k_steps

Class Solution

java.lang.Object

g2301_2400.s2400_number_of_ways_to_reach_a_position_after_exactly_k_steps.Solution

public class Solution
extends Object

2400 - Number of Ways to Reach a Position After Exactly k Steps.

Medium

You are given two positive integers startPos and endPos. Initially, you are standing at position startPos on an infinite number line. With one step, you can move either one position to the left, or one position to the right.

Given a positive integer k, return the number of different ways to reach the position endPos starting from startPos_, such that you perform exactly_ k steps. Since the answer may be very large, return it modulo 109 + 7.

Two ways are considered different if the order of the steps made is not exactly the same.

Note that the number line includes negative integers.

Example 1:

Input: startPos = 1, endPos = 2, k = 3

Output: 3

Explanation: We can reach position 2 from 1 in exactly 3 steps in three ways:

• 1 -> 2 -> 3 -> 2.

• 1 -> 2 -> 1 -> 2.

• 1 -> 0 -> 1 -> 2.

It can be proven that no other way is possible, so we return 3.

Example 2:

Input: startPos = 2, endPos = 5, k = 10

Output: 0

Explanation: It is impossible to reach position 5 from position 2 in exactly 10 steps.

Constraints:

• 1 <= startPos, endPos, k <= 1000

Constructor Summary

Constructors

Constructor and Description
Solution()

Method Summary

Modifier and Type	Method and Description
int	numberOfWays(int startPos, int endPos, int k)

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

numberOfWays

public int numberOfWays(int startPos,
                        int endPos,
                        int k)