70. Climbing Stairs

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?

题意:n阶台阶，每次爬1阶或2阶，问有多少种爬法。

思路：动态规划：f(n) = f(n-1)+f(n-2) （即走一步还是走两步到达n）。

class Solution {public:    int climbStairs(int n) {        if(0 == n)            return 0;        vector<int> f(n+1, 0);        f[1] = 1;        f[2] = 2;        for(int i=3;i<=n;i++)            f[i] = f[i-1]+f[i-2];        return f[n];    }};