leetcode/70.climbing-stairs.java at master · ShawnLi1014/leetcode · GitHub

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/*
 * @lc app=leetcode id=70 lang=java
 *
 * [70] Climbing Stairs
 *
 * https://leetcode.com/problems/climbing-stairs/description/
 *
 * algorithms
 * Easy (44.65%)
 * Likes:    2432
 * Dislikes: 88
 * Total Accepted:    438.4K
 * Total Submissions: 981.9K
 * Testcase Example:  '2'
 *
 * You are climbing a stair case. It takes n steps to reach to the top.
 *
 * Each time you can either climb 1 or 2 steps. In how many distinct ways can
 * you climb to the top?
 *
 * Note: Given n will be a positive integer.
 *
 * Example 1:
 *
 *
 * Input: 2
 * Output: 2
 * Explanation: There are two ways to climb to the top.
 * 1. 1 step + 1 step
 * 2. 2 steps
 *
 *
 * Example 2:
 *
 *
 * Input: 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
 *
 *
 */
class Solution {
    public int climbStairs(int n) {
        int[] dp = new int[n + 1];
        for (int i = 1; i < n + 1; i++) {
            if (i == 1 || i == 2) {
                dp[i] = i;
            } else {
                dp[i] = dp[i - 1] + dp[i - 2];
            }
        }
        return dp[n];
    }
}