LeetCode - 70. 爬楼梯

class Solution {

/**
* f(n) 表示爬到第n层的方法数
* 第n层可由第n-1层迈1步到达
* 亦可由第n-2层迈2步到达
* 所以 f(n) = f(n-1) + f(n-2)
* @param n
* @return
*/
public int climbStairs(int n) {
if (n == 1) {
return 1;
}
if (n == 2) {
return 2;
}

int a = 1, b = 2, c = 3;

for (int i = 3; i <= n; ++ i) {
c = a + b;
a = b;
b = c;
}

return c;
}
}