Solving this recurrence relation: T(n) = 2 T(n/2) + f(n).
时间: 2024-05-27 17:11:40 浏览: 82
计算2的n次方
5星 · 资源好评率100%
To solve this recurrence relation, we can use the Master Theorem.
The recurrence relation can be written in the form:
T(n) = aT(n/b) + f(n)
where a = 2, b = 2, and f(n) = f(n).
We can use the following steps to apply the Master Theorem:
1. Calculate the value of logb(a):
log2(2) = 1
2. Compare f(n) with nlogb(a):
If f(n) = O(nlogb(a)-ε) for some ε > 0, then T(n) = Θ(nlogb(a)).
If f(n) = Θ(nlogb(a)), then T(n) = Θ(nlogb(a) log n).
If f(n) = Ω(nlogb(a)+ε) for some ε > 0, and if af(n/b) ≤ cf(n) for some constant c < 1 and sufficiently large n, then T(n) = Θ(f(n)).
In this case, we have f(n) = f(n), which is not comparable to nlogb(a) = n. Therefore, we cannot use the Master Theorem to determine the asymptotic growth rate of T(n).
However, we can still solve the recurrence relation by using the substitution method.
Let T(n) = 2T(n/2) + f(n)
Assume that T(n) = O(nlog n).
Then, we have:
T(n) ≤ 2T(n/2) + f(n)
≤ 2(c(n/2)log(n/2)) + f(n)
= cnlogn - cn + f(n)
Since f(n) is a non-negative function, we can further simplify:
T(n) ≤ cnlogn + f(n)
Therefore, T(n) = O(nlogn) is a valid upper bound.
Now, assume that T(n) = Ω(nlogn).
Then, we have:
T(n) ≥ 2T(n/2) + f(n)
≥ 2(c(n/2)log(n/2)) + f(n)
= cnlogn - cn + f(n)
Since f(n) is a non-negative function, we can further simplify:
T(n) ≥ cnlogn + f(n)
Therefore, T(n) = Ω(nlogn) is a valid lower bound.
Combining the upper and lower bounds, we get:
T(n) = Θ(nlogn)
Therefore, the solution to the recurrence relation is T(n) = Θ(nlogn).
阅读全文