题意:给定$x, n$满足$1 \leq x, n \leq 1000000$,求$\sum{(x^a-1,x^b-1)}$对$1e9+7$取模后的值,其中$1 \leq a, b \leq n$. 分析:首先不难有$(x^a - 1, x ^ b - 1) = x^{(a,b)}-1$(证明方法可沿欧几里得定理思路),那么我们只需要考虑$(a,b) = d$即可,设$f(d)$为使得$(a, b) = d$的对数,那么不难有$ans = \sum_{d = 1}^{n}{f(d)(x^d-1)…

GCD Time Limit: 10000/5000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)Total Submission(s): 2742    Accepted Submission(s): 980 Problem Description Give you a sequence of N(N≤100,000) integers : a1,...,an(0<ai≤1000,000,000). There ar…

GCD is Funny 题目连接: http://acm.hdu.edu.cn/showproblem.php?pid=5902 Description Alex has invented a new game for fun. There are n integers at a board and he performs the following moves repeatedly: He chooses three numbers a, b and c written at the boa…

GCD Time Limit: 6000/3000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 4272    Accepted Submission(s): 1492 Problem Description Given 5 integers: a, b, c, d, k, you're to find x in a...b, y in c...d that GCD(x, y)…

GCD 题目连接: http://acm.hdu.edu.cn/showproblem.php?pid=1695 Description Given 5 integers: a, b, c, d, k, you're to find x in a...b, y in c...d that GCD(x, y) = k. GCD(x, y) means the greatest common divisor of x and y. Since the number of choices may be…

GCD and LCM Time Limit: 20 Sec Memory Limit: 256 MB 题目连接 http://acm.hdu.edu.cn/showproblem.php?pid=4497 Description Given two positive integers G and L, could you tell me how many solutions of (x, y, z) there are, satisfying that gcd(x, y, z) = G and…

题目链接:http://acm.hdu.edu.cn/showproblem.php?pid=4675 题意:给出n,m,K,一个长度为n的数列A(1<=A[i]<=m).对于d(1<=d<=m),有多少个长度为n的数列B满足: (1)1<=B[i]<=m; (2)Gcd(B[1],B[2],……,B[n])=d: (3)恰有K个位置满足A[i]!=B[i]. 思路: i64 p[N]; void init(){    p[0]=1;    int i;    FOR1…

题目链接:http://acm.hdu.edu.cn/showproblem.php?pid=5726 给你n个数,q个询问,每个询问问你有多少对l r的gcd(a[l] , ... , a[r]) 等于的gcd(a[l'] ,..., a[r']). 先用RMQ预处理gcd,dp[i][j] 表示从i开始2^j个数的gcd. 然后用map存取某个gcd所对应的l r的数量. 我们可以在询问前进行预处理,先枚举i,以i为左端点的gcd(a[i],..., a[r])的种类数不会超过log2(n)…

[题目链接] http://acm.hdu.edu.cn/showproblem.php?pid=5726 [题目大意] 给出数列An,对于询问的区间[L,R],求出区间内数的GCD值,并且求出GCD值与其相等的区间总数 [题解] 首先,固定一个区间的右端点,利用GCD的递减性质,可以求出GCD相等的区间左端点的范围,将其范围的左右端点保存下来,同时,对于每个新产生的区间,以其GCD值为下标的MAP值+1,最后对于每个询问,在其右端点保存的范围中查找,获得其GCD值,同时在MAP中获取该GCD值…

题目链接:http://acm.hdu.edu.cn/showproblem.php?pid=1695 题意:x位于区间[a, b],y位于区间[c, d],求满足GCD(x, y) = k的(x, y)有多少组,不考虑顺序. 思路:a = c = 1简化了问题,原问题可以转化为在[1, b/k]和[1, d/k]这两个区间各取一个数,组成的数对是互质的数量,不考虑顺序.我们让d > b,我们枚举区间[1, d/k]的数i作为二元组的第二位,因为不考虑顺序我们考虑第一位的值时,只用考虑小于i的情…