分别使用FIFO、OPT、LRU三种置换算法来 模拟页面置换的过程的代码’

以下是使用FIFO、OPT、LRU三种置换算法来模拟页面置换的Python代码示例：

FIFO算法：

def fifo(pages, frames):
    frame_list = []
    page_faults = 0
    pointer = 0
    for i in range(frames):
        frame_list.append(None)
    for page in pages:
        if page not in frame_list:
            frame_list[pointer] = page
            pointer = (pointer + 1) % frames
            page_faults += 1
    return page_faults

OPT算法：

def opt(pages, frames):
    frame_list = []
    page_faults = 0
    for i in range(frames):
        frame_list.append(None)
    for i in range(len(pages)):
        if pages[i] not in frame_list:
            if None in frame_list:
                frame_list[frame_list.index(None)] = pages[i]
            else:
                distances = []
                for j in range(frames):
                    try:
                        distances.append(pages[i+1:].index(frame_list[j]))
                    except ValueError:
                        distances.append(len(pages))
                frame_list[distances.index(max(distances))] = pages[i]
            page_faults += 1
    return page_faults

LRU算法：

def lru(pages, frames):
    frame_list = []
    page_faults = 0
    for i in range(frames):
        frame_list.append(None)
    for page in pages:
        if page not in frame_list:
            if None in frame_list:
                frame_list[frame_list.index(None)] = page
            else:
                lru_index = -1
                for i in range(frames):
                    if frame_list[i] in pages[pages.index(page):]:
                        if lru_index == -1:
                            lru_index = i
                        elif pages[pages.index(frame_list[i]):pages.index(page)].count(frame_list[i]) < pages[pages.index(frame_list[lru_index]):pages.index(page)].count(frame_list[lru_index]):
                            lru_index = i
                frame_list[lru_index] = page
            page_faults += 1
        else:
            frame_list.remove(page)
            frame_list.append(page)
    return page_faults