class ExpressNumber {
public int CountWays(int n) {
// bottom up
int n0 = 1, n1 = 1, n2 = 1, n3 = 2;
for(int i = 4; i <= n; i++){
int temp = n0 + n1 + n3;
n0 = n1;
n1 = n2;
n2 = n3;
n3 = temp;
}
return n3;
}
public static void main(String[] args) {
ExpressNumber en = new ExpressNumber();
System.out.println(en.CountWays(4));
System.out.println(en.CountWays(5));
System.out.println(en.CountWays(6));
}
}
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Course: https://www.educative.io/collection/5668639101419520/5633779737559040
Lesson: https://www.educative.io/collection/page/5668639101419520/5633779737559040/5724313353191424