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Climbing Stairs Problem | ||
This program provides a solution to the "Climbing Stairs" problem, a classic example of dynamic programming. The problem can be stated as follows: | ||
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Problem Statement: | ||
A person is at the bottom of a staircase with n steps and wants to reach the top. They can take either 1 or 2 steps at a time. The task is to determine the number of distinct ways the person can reach the top of the staircase. | ||
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Approach:s | ||
Dynamic Programming | ||
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This problem has overlapping subproblems, making it a suitable candidate for dynamic programming. | ||
Define dp[i] as the number of ways to reach the i-th step. | ||
The number of ways to reach step i is the sum of ways to reach the previous step i-1 and the step before that, i-2. This is because the person can arrive at step i by taking a single step from i-1 or a double step from i-2. | ||
Thus, the recurrence relation is: | ||
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𝑑𝑝[𝑖]=𝑑𝑝[𝑖−1]+𝑑𝑝[𝑖−2]dp[i]=dp[i−1]+dp[i−2] | ||
Base Cases: | ||
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If there are no steps (n = 0), there is 1 way (doing nothing). | ||
If there is one step (n = 1), there is also 1 way to reach it. | ||
Building the Solution: | ||
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Create an array dp of size n+1 to store the number of ways to reach each step up to n. | ||
Initialize dp[0] = 1 and dp[1] = 1 as per the base cases. | ||
Use a loop to fill the array from dp[2] up to dp[n] using the recurrence relation. | ||
Finally, dp[n] will contain the number of distinct ways to reach the top of the staircase with n steps. | ||
Example: | ||
For n = 5, the program calculates the ways as follows: | ||
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dp[0] = 1 | ||
dp[1] = 1 | ||
dp[2] = dp[1] + dp[0] = 2 | ||
dp[3] = dp[2] + dp[1] = 3 | ||
dp[4] = dp[3] + dp[2] = 5 | ||
dp[5] = dp[4] + dp[3] = 8 | ||
So, there are 8 distinct ways to reach the 5th step. | ||
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Complexity Analysis: | ||
Time Complexity: O(n) because we only need to compute each value in dp from 0 to n. | ||
Space Complexity: O(n) for storing the dp array. | ||
This dynamic programming approach efficiently computes the number of ways to climb the staircase, demonstrating how overlapping subproblems and optimal substructure can be leveraged to solve problems effectively. |
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#include <stdio.h> | ||
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int climbStairs(int n) | ||
{ | ||
if (n == 0 || n == 1) | ||
{ | ||
return 1; | ||
} | ||
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int dp[n + 1]; | ||
dp[0] = dp[1] = 1; | ||
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for (int i = 2; i <= n; i++) | ||
{ | ||
dp[i] = dp[i - 1] + dp[i - 2]; | ||
} | ||
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return dp[n]; | ||
} | ||
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int main() | ||
{ | ||
int n = 5; // Example input | ||
printf("Ways to climb %d stairs: %d\n", n, climbStairs(n)); | ||
return 0; | ||
} |