E. XOR and Favorite Number（莫队算法）
E. XOR and Favorite Number
time limit per test
4 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
Bob has a favorite number k and ai of length n. Now he asks you to answer m queries. Each query is given by a pair li and ri and asks you to count the number of pairs of integers i and j, such that l ≤ i ≤ j ≤ r and the xor of the numbers ai, ai + 1, ..., aj is equal to k.
Input
The first line of the input contains integers n, m and k (1 ≤ n, m ≤ 100 000, 0 ≤ k ≤ 1 000 000) — the length of the array, the number of queries and Bob's favorite number respectively.
The second line contains n integers ai (0 ≤ ai ≤ 1 000 000) — Bob's array.
Then m lines follow. The i-th line contains integers li and ri (1 ≤ li ≤ ri ≤ n) — the parameters of the i-th query.
Output
Print m lines, answer the queries in the order they appear in the input.
Sample test(s)
input
6 2 3 1 2 1 1 0 3 1 6 3 5
output
7 0
input
5 3 1 1 1 1 1 1 1 5 2 4 1 3
output
9 4 4
Note
In the first sample the suitable pairs of i and j for the first query are: (1, 2), (1, 4), (1, 5), (2, 3), (3, 6), (5, 6), (6, 6). Not a single of these pairs is suitable for the second query.
In the second sample xor equals 1 for all subarrays of an odd length.
题意：有n个数和m次查询，每次查询区间[l, r]问满足ai ^ ai+1 ^ ... ^ aj == k的(i, j) (l <= i <= j <= r)有多少对。
利用前缀和的思想在传入值num的时候就计算异或（num[i]=num[i]^num[i-1]）;类似sum[i]=sum[i-1]+a[i]，对于add与del函数
由于，pre[]<--->flag[] 中保存的是前缀和，所以num[x]^k的位置就是满足能亦或等到 K 的所有对数所在的位置，所以有flag[num[x]^k]。
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