procedure three-way-partition(A : array of values, mid : value): i ← 0 j ← 0 k ← size of A - 1

while j <= k:
    if A[j] < mid:
        swap A[i] and A[j]
        i ← i + 1
        j ← j + 1
    else if A[j] > mid:
        swap A[j] and A[k]
        k ← k - 1
    else:
        j ← j + 1