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 Object

2400 - Number of Ways to Reach a Position After Exactly k Steps.<p>Medium</p> <p>You are given two <strong>positive</strong> integers <code>startPos</code> and <code>endPos</code>. Initially, you are standing at position <code>startPos</code> on an <strong>infinite</strong> number line. With one step, you can move either one position to the left, or one position to the right.</p> <p>Given a positive integer <code>k</code>, return <em>the number of <strong>different</strong> ways to reach the position</em> <code>endPos</code> <em>starting from</em> <code>startPos</code><em>, such that you perform <strong>exactly</strong></em> <code>k</code> <em>steps</em>. Since the answer may be very large, return it <strong>modulo</strong> <code>10⁹ + 7</code>.</p> <p>Two ways are considered different if the order of the steps made is not exactly the same.</p> <p><strong>Note</strong> that the number line includes negative integers.</p> <p><strong>Example 1:</strong></p> <p><strong>Input:</strong> startPos = 1, endPos = 2, k = 3</p> <p><strong>Output:</strong> 3</p> <p><strong>Explanation:</strong> We can reach position 2 from 1 in exactly 3 steps in three ways:</p> <ul> <li> <p>1 -> 2 -> 3 -> 2.</p> </li> <li> <p>1 -> 2 -> 1 -> 2.</p> </li> <li> <p>1 -> 0 -> 1 -> 2.</p> </li> </ul> <p>It can be proven that no other way is possible, so we return 3.</p> <p><strong>Example 2:</strong></p> <p><strong>Input:</strong> startPos = 2, endPos = 5, k = 10</p> <p><strong>Output:</strong> 0</p> <p><strong>Explanation:</strong> It is impossible to reach position 5 from position 2 in exactly 10 steps.</p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= startPos, endPos, k <= 1000</code></li> </ul>

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)