leetcode70. Climbing Stairs

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?

Note: Given n will be a positive integer.

解法一

way[i] = way[i - 1] + way[i - 2]

public class Solution {
public int climbStairs(int n) {
int[] way = new int
;
if (n == 1) {
way[0] = 1;
}
if (n > 1) {
way[0] = 1;
way[1] = 2;
}
for (int i = 2; i < n; i++) {
way[i] = way[i - 1] + way[i - 2];
}

return way[n - 1];
}
}

解法二

fibonacci.

public class Solution {
public int climbStairs(int n) {
if (n < 0) {
return 0;
}
if (n == 0 || n == 1 || n == 2) {
return n;
}
int one_step_before = 2;
int two_step_before = 1;
int all_ways = 0;
for (int i = 2; i < n; i++) {
all_ways = one_step_before + two_step_before;
two_step_before = one_step_before;
one_step_before = all_ways;
}

return all_ways;
}
}