Created
July 6, 2013 09:09
-
-
Save jimexist/5939327 to your computer and use it in GitHub Desktop.
Solution in Java to solve the Climb Stairs problem in Leetcode.com
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
public class Solution { | |
private Map<Integer, int[]> pows = new HashMap<Integer, int[]>(); | |
{ | |
pows.put(1, new int[]{1, 1, 1, 0}); | |
} | |
private int[] pow(int n) { | |
if (pows.containsKey(n)) return pows.get(n); | |
int[] r = sqr(pow(n/2)); | |
if (n % 2 == 1) { | |
r = mult(r, pows.get(1)); | |
} | |
pows.put(n, r); | |
return r; | |
} | |
private int[] sqr(int[] a) { | |
return mult(a, a); | |
} | |
private int[] mult(int[] a, int [] b) { | |
int[] c = new int[4]; | |
c[0] = a[0]*b[0] + a[1]*b[2]; | |
c[1] = a[0]*b[1] + a[1]*b[3]; | |
c[2] = a[2]*b[0] + a[3]*b[2]; | |
c[3] = a[2]*b[1] + a[3]*b[3]; | |
return c; | |
} | |
public int climbStairs(int n) { | |
if (n == 1) return 1; | |
if (n == 2) return 2; | |
int[] matrix = pow(n-2); | |
return 2*matrix[0] + matrix[1]; | |
} | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment