C++
1 class Solution { 2 public: 3 /** 4 * @param n: An integer 5 * @return: An integer 6 */ 7 int climbStairs(int n) { 8 // write your code here 9 // f(0) = 1; 10 // f(1) = 1; 11 // f(2) = 2; 12 // f(n) = f(n-1) + f(n-2) n>2; 13 if (n == 2) { 14 return 2; 15 } 16 if (n == 0 || n == 1) { 17 return 1; 18 } 19 int a=1, b=2; 20 //int c; 21 for (int i=3; i<=n; i++) { 22 b = a + b; 23 a = b - a; 24 // c = a + b; 25 // a = b; 26 // b = c; 27 } 28 return b; 29 } 30 };