Package 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 java.lang.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
    Description
    Solution()
     

  • Method Summary

    Modifier and Type
    Method
    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 Details

    • Solution

      public Solution()

  • Method Details

    • numberOfWays

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