70. Climbing Stairs (Easy)

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?

爬楼梯问题，爬到第n层的可能是：从第n-1层爬到第n层（一步），或者从第n-2层爬到第n层（两步）。所以计算公式为：f(n) = f(n-1) + f(n-2)，其实就是斐波拉契数列。

Solutions:

C:

方法一：递归。效率比较低，但代码简单且容易理解。

int climbStairs(int n) {
if(n == 0 || n == 1) {
return 1;
}
if(n == 2) {
return 2;
}
return climbStairs(n - 1) + climbStairs(n - 2);
}

方法二：不用递归，每计算一步都保存该步的结果：

int climbStairs(int n) {
if(n == 0 || n == 1) {
return 1;
}
if(n == 2) {
return 2;
}
int a = 1;
int b = 2;
int c;
for(int i = 3; i <= n; i++) {
c = a + b;
a = b;
b = c;
}
return c;
}