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. 1 step + 1 step 2. 2 steps
Example 2:
Input: n = 3
Output: 3
Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step
Constraints:
1 <= n <= 45
Solution
#include <vector>
class Solution {
public:
int climbStairs(int n) {
if (n < 2) {
return n;
}
std::vector<int> cache(n);
// Creating a cache or DP to store the result
// so that we don't have to iterate multiple times
// for the same values.
// For 0 and 1 the result array i.e cache values would be 1 and 2
// In loop we are just getting ith values i.e 5th step values from
// i-1 and i-2 which are 4th step and 3rd step values.
cache[0] = 1;
cache[1] = 2;
for (int i = 2; i < n; i++) {
cache[i] = cache[i - 1] + cache[i - 2];
}
return cache[n - 1];
}
};