01-Climbing-Stairs.md

Climbing Stairs

Problem Link

https://leetcode.com/problems/climbing-stairs/

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Pattern

• 1D DP

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Approach

Each step can be reached from the previous one or the one before that, so compute the Fibonacci-style recurrence.

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Time Complexity

O(n)

Space Complexity

O(1)

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Java Solution

class Solution {
    public int climbStairs(int n) {
        if (n <= 2) return n;
        int first = 1, second = 2;
        for (int i = 3; i <= n; i++) {
            int current = first + second;
            first = second;
            second = current;
        }
        return second;
    }
}