Too_Much.md

Too Much

I found a program that generates the flag of this challenge, but the implementation of one of its functions is not available. This function seems simple, but I am confused because of the large number of numbers! Can you help me find the flag before the competition is over?!

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题目给了一个包含1000000个数字的文件numbers.txt,要求编写一个函数:对于给定的x,在numbers.txt中找到两个数y和z,要求满足y != z 和 (y + z) == x,返回不重复的(y,z)的个数.

利用哈希数组的思想,将时间复杂度降到O(n):

def func2(x):
    """
    Returns the number of distinct pairs (y, z) from the numbers in the file "numbers.txt" whose y != z and (y + z) == x
    Note that two pairs (y, z) and (z, y) are considered the same and are counted only once
    """
    with open('numbers.txt', 'r') as f:
        data = [int(_) for _ in f.readlines()]

    length = max(data) + 1
    hash_arr = [False] * (length)

    for t in data:
        hash_arr[t] = True
    ans = 0
    for y in data:
        z = x-y
        if z > 0 and hash_arr[z]:
            if y != z:
                ans += 1
    print(chr(ans//2))
    return ans // 2

def get_flag(res):
    flag = []
    for i in range(len(res)):
        flag.append(chr(func2(res[i])))
    flag = ''.join(flag)
    return flag

if __name__ == "__main__":
    res = [751741232, 519127658, 583555720, 3491231752, 3333111256, 481365731, 982100628, 1001121327, 3520999746,
           915725624, 3218509573, 3621224627, 3270950626, 3321456817, 3091205444, 999888800, 475855017, 448213157,
           3222412857, 820711846, 3710211491, 3119823672, 3333211607, 812955676, 971211391, 3210953872, 289789909,
           781213400, 578265122, 910021887, 653886578, 3712776506, 229812345, 582319118, 1111276998, 1151016390,
           700123328, 1074521304, 3210438183, 817210125, 501231350, 753244584, 3240911853, 415234677, 469125436,
           592610671, 612980665, 291821367, 344199617, 1011100412, 681623864, 897219249, 3132267885, 565913000,
           301203203, 3100544737, 432812663, 1012813485, 510928797, 671553831, 3216409218, 3191288433, 698777123,
           3512778698, 810476845, 3102989588, 3621432709, 812321695, 526486561, 378912454, 3316207359, 623111580,
           344209171, 537454826, 691277475, 2634678623, 1112182335, 792111856, 762989676, 666210267, 871278369,
           581009345, 391231132, 921732469, 717217468, 3101412929, 3101217354, 831912337, 532666530, 701012510,
           601365919, 492699680, 2843119525]
    print("The flag is", get_flag(res))

The flag is TMUCTF{r4nd0m_fl46_f0r_fun!_SzC!$JvnbrRh6kc*1@L!4vMueH1k0xKPJem@vh6Y2&Sb2CJzwjnTfU6wVZyePOK3}

flag:TMUCTF{r4nd0m_fl46_f0r_fun!_SzC!$JvnbrRh6kc*1@L!4vMueH1k0xKPJem@vh6Y2&Sb2CJzwjnTfU6wVZyePOK3}