Climbing Stairs
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1 public class Solution { 2 public int climbStairs(int n) { 3 int f1 = 2; 4 int f2 = 1; 5 if(n<=0) return 0; 6 if(n==1) return f2; 7 if(n==2) return f1; 8 int fn=0; 9 for(int i=2;i<n;i++){ 10 fn=f1+f2; 11 f2=f1; 12 f1=fn; 13 } 14 return fn; 15 } 16 }