排序算法之二分治法

MERGE(A,p,q,r)
n₁ = q-p+1
n₂ = r-q
let L[1..n_1+1] and R[1..n_2+1] be new arrays
for i = 1 to n_1
　　L[i] = A[p+i-1]
for j = 1 to n_2
　　R[j] = A[q+j]
L[n_1+1] = \infty
R[n_2+1] = \infty
i = 1
j = 1
for k = p to r
　　ifL[i] \leq R[j]
　　　　A[k] = L[i]
　　　　i = i+1
else A[k] = R[j]
　　　　j = j+1

MERGE-SORT(A.p,r)
if p<r
　　q = |(p+r)/2|
MERGE-SORT(A,p,q)
MERGE-SORT(A,q+1,r)
MERGE(A,p,q.r)