标签：style blog http color io 使用 ar for strong
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?
这是最简单的DP了，递推公式为f(n)=f(n-1)+f(n-2)
因此建立vector存放中间结果即可。
class Solution { public: int climbStairs(int n) { vector<int> v; for(int i = 0; i <= n; i ++) { if(i == 0) v.push_back(1); else if(i == 1) v.push_back(1); else v.push_back(v[i-2]+v[i-1]); } return v[n]; } };
其实可以改进一下减少空间复杂度。
每个元素仅依赖于前两个元素，因此没有必要使用vector保存所有中间结果，只需要保存前两个。
class Solution { public: int climbStairs(int n) { if(n <= 1) return 1; int pre1 = 1; //n==0 int pre2 = 1; //n==1 for(int i = 2; i <= n; i ++) { int cur = pre1+pre2; pre1 = pre2; pre2 = cur; } return pre2; } };
【LeetCode】Climbing Stairs (2 solutions)
标签：style blog http color io 使用 ar for strong
原文地址：http://www.cnblogs.com/ganganloveu/p/4026545.html
