LeetCode 70. Climbing Stairs

[Woodyiiiiiii]

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

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class Solution {
    public int climbStairs(int n) {
        int[] dp = new int[n + 2];
        dp[1] = dp[2] = 1;
        
        for (int i = 3; i <= n + 1; ++i) {
            dp[i] = dp[i - 1] + dp[i - 2];
        }
        
        return dp[n + 1];
    }
}

如果按照“标准”格式，可以这样写：

class Solution {
    public int climbStairs(int n) {
        int[] dp = new int[n + 2];
        dp[1] = dp[2] = 1;
        
        for (int i = 3; i <= n + 1; ++i) {
            for (int way = 1; way <= 2; ++way) {
                dp[i] += dp[i - way];
            }
        }
        
        return dp[n + 1];
    }
}

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参考资料:
LeetCode原题