_0070ClimbingStairs.java

package com.heatwave.leetcode.problems;

/**
 * You are climbing a staircase. It takes n steps to reach the top.
 * <p>
 * Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
 * <p>
 *  
 * <p>
 * Example 1:
 * <p>
 * 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:
 * <p>
 * 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
 *  
 * <p>
 * Constraints:
 * <p>
 * 1 <= n <= 45
 * <p>
 * 来源：力扣（LeetCode）
 * 链接：https://leetcode.cn/problems/climbing-stairs
 * 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。
 */
public class _0070ClimbingStairs {
    static class Solution {
        public int climbStairs(int n) {
            int[] dp = new int[n + 1];

            if (n == 1) {
                return 1;
            } else if (n == 2) {
                return 2;
            }

            dp[0] = 0;
            dp[1] = 1;
            dp[2] = 2;

            for (int i = 3; i <= n; i++) {
                dp[i] = dp[i - 1] + dp[i - 2];
            }

            return dp[n];
        }
    }
}