Codeforce Round #506 DIV3

Codeforce Round #506 Div3

A Many Euqal Substrings

题意： 就是求字符串的最长前缀后缀匹配子串

题解： 利用KMP算法求next数组，nxet[len[t]]可能就是最长前缀后缀匹配长度，再做下判断就好了

时间复杂度O(n), n 为字符串的长度

# -*- coding: utf-8 -*-



def get_next(t, nxt):
    t = ' ' + t
    i = 1
    j = 0
    nxt[1] = 0
    m = len(t) - 1
    while i < m:
        if j == 0 or t[i] == t[j]:
            i += 1
            j += 1
            nxt[i] = j
        else:
            j = nxt[j]
    return nxt[m]


n, k = map(int, input().split())
t = str(input())
nxt = [0] * (len(t) + 1)
length = get_next(t, nxt)
if t[length - 1] != t[-1]:
    if t[0] == t[-1]:
        length = 1
    else:
        length = 0
print(t[0:n - length] * k + t[n - length:n])

B Creating the Contest

B题比A题要简单些，贪心一下就好了

def work(n, a):
    tmp = 1
    maxV = 1
    for i in range(1, n):
        if a[i] <= a[i - 1] * 2:
            tmp += 1
        else:
            maxV = max(maxV, tmp)
            tmp = 1
    return max(maxV, tmp)


n = int(input())
a = tuple(map(int, input().split()))
print(work(n, a))

C Maximal Intersection

我做这道题比做A题用的时间短些，这道题就是排序，完了之后

__答案就是：__max(r[0] - l[-2], r[1] - l[-1])，若(l[-1], r[0])是一个片段，再更新一下期望的结果

def work(n, a, b):
    a_ = a[:]
    b_ = b[:]
    a.sort()
    b.sort()
    ans = max(b[0] - a[-2], b[1] - a[-1])
    for i in range(n):
        if a[-1] == a_[i] and b[0] == b_[i]:
            ans = max(b[1] - a[-2], ans)
            break
    return ans if ans >= 0 else 0


n = int(input())
a = []
b = []
for i in range(n):
    l, r = map(int, input().split())
    a.append(l)
    b.append(r)
print(work(n, a, b))

D Concatenated Multiples

选择pypy提交时，比选择python快多了

def: main():
    # PyPy is fast, compliant 
    n, k = map(int, input().split())
    aa, cnt, res = [], {}, 0
    scale = [10 ** i + 1 for i in range(11)]
    for w in input().split():
        a, s = int(w), len(w)
        aa.append(a)
        if not a * scale[s] % k:
            res -= 1
        t = (s, a % k)
        cnt[t] = cnt.get(t, 0) + 1
    scale = [1 - i for i in scale]
    for a in aa:
        for s in range(1, 11):
            x = a * scale[s] % k
            res += cnt.get((s, x), 0)
    print(res)


if __name__ == '__main__':
    main()

python学习总结

做这几道题练手python，遇到的几个问题

• 数组复制用[:], 直接用 = 是传引用，函数参数传递类似于java
• 三目运算符不同于C语言，真值 if 成立 else 假值
• input一次读一行，tuple数组，list列表，dict字典。map()返回值类型是list
• python无自增自减运算符，因为自增自减改变对象本身，学习C++重载自增自减运算符时可以理解这一点。+= 改变了变量。python模型规定数值对象是不可改变的。