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?

思路：

直接用递归超时了，所以之后用了斐波那契数列。

超时：

public static int climbStairs(int n) {
if (n <= 3) {
return n;
}
return calculate(n);
}

private static int calculate(int n) {
if (n < 0) {
return 0;
}
if (n == 0) {
return 1;
}
return calculate(n - 1) + calculate(n - 2);
}
斐波那契：

public class Solution {
public int climbStairs(int n) {
if (n <= 3) {
return n;
}
int x = 1, y = 1;
while (n > 0) {
y += x;
x = y - x;
n--;
}
return x;
}

}