Codeforces Round #365 (Div. 2) D. Mishka and Interesting sum 树状数组

D. Mishka and Interesting sum

链接:

http://codeforces.com/problemset/problem/703/D

题意：

给一个序列 每次询问一个区间 求区间中出现次数为偶数次的数的异或和

代码：

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<map>
using namespace std;

struct Query {
    int l, r, id;
    bool operator<(const Query &a)const {
        return r < a.r;
    }
};

const int maxn = 1000000 + 10;
int a[maxn], pre[maxn], ans[maxn], tree[maxn];
Query q[maxn];

void add(int k, int num)
{
    while (k < maxn){
        tree[k] ^= num;
        k += k&-k;
    }
}

int sum(int k)
{
    int sum = 0;
    while (k){
        sum ^= tree[k];
        k -= k&-k;
    }
    return sum;
}

int main() 
{
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        scanf("%d", &a[i]);
        pre[i] = pre[i - 1] ^ a[i];
    }
    int m;
    cin >> m;
    for (int i = 1; i <= m; i++) {
        scanf("%d%d", &q[i].l, &q[i].r);
        q[i].id = i;
    }
    sort(q + 1, q + 1 + m);
    map<int, int>vis;
    int t = 1;
    for (int i = 1; i <= n; i++) {
        if (vis[a[i]])
            add(vis[a[i]], a[i]);
        vis[a[i]] = i;
        add(i, a[i]);
        while (q[t].r <= i && t <= m) {
            int l = q[t].l - 1, r = q[t].r;
            ans[q[t].id] = sum(l) ^ sum(r) ^ pre[l] ^ pre[r];
            t++;
        }
    }
    for (int i = 1; i <= m; i++) 
        printf("%d
", ans[i]);
    return 0;
}