【LeetCode】070. Climbing Stairs

题目：

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.

题解：

　　爬到第n层的方法要么是从第n-1层一步上来的，要不就是从n-2层2步上来的

Solution 1 ()

class Solution {

public:

    int climbStairs(int n) {

        vector<int> dp(n,);

        if(n<) return n;

        dp[] = ;

        dp[] = ;

        for(int i=; i<n; i++) {

            dp[i] = dp[i-] + dp[i-];

        }

        return dp[n-];

    }

};

Solution 2 ()

class Solution {

public:

    int climbStairs(int n) {

        if(n<) return n;

        int a = ;

        int b = ;

        for(int i=; i<n; i++) {

            b += a;

            a = b - a;

        }

        return b;

    }

};

Solution 2

class Solution {

public:

    int climbStairs(int n) {

        const double t = sqrt();

        return floor((pow(( + t) / , n + ) + pow(( - t) / , n + )) / t + 0.5);

    }

};

斐波那契数列通项公式

巴特西

【LeetCode】070. Climbing Stairs

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