LeetCode-in-All
70. Climbing Stairs
Easy
You are climbing a staircase. It takes n steps to reach the top.
Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
Example 1:
Input: n = 2
Output: 2
Explanation: There are two ways to climb to the top.
-
1 step + 1 step
-
2 steps
Example 2:
Input: n = 3
Output: 3
Explanation: There are three ways to climb to the top.
-
1 step + 1 step + 1 step
-
1 step + 2 steps
-
2 steps + 1 step
Constraints:
1 <= n <= 45
Solution
#include <stdio.h>
#include <stdlib.h>
int climbStairs(int n) {
if (n < 2) {
return n;
}
// Create an array to store the number of ways to climb to each step
int* cache = (int*)malloc(n * sizeof(int));
// Base cases
cache[0] = 1; // 1 way to climb to the 1st step
cache[1] = 2; // 2 ways to climb to the 2nd step
// Fill the cache using dynamic programming
for (int i = 2; i < n; i++) {
cache[i] = cache[i - 1] + cache[i - 2];
}
// Store the result
int result = cache[n - 1];
// Free allocated memory
free(cache);
return result;
}