class Solution {

public int climbStairs(int n) {

if(n <= 0) return 0;

if(n <= 2) return n;

int[] d = new int[n];

d[0] = 1;

d[1] = 2;

for(int i = 2; i < n; i++) {

d[i] = d[i-1] + d[i-2];

}

return d[n-1];

}

}

// fibnaci way

class Solution {

public int climbStairs(int n) {

if(n <= 0) return 0;

if(n <= 2) return n;

int f = 1;

int s = 2;

int t = 0;

for(int i = 2; i < n; i++) {

t = f+s;

f = s;

s = t;

}

return t;

}

}