线段树区间异或

The Preliminary Contest for ICPC Asia Shanghai 2019 B题
超内存了

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#define lch(x) x<<1
#define rch(x) x<<1|1
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
using namespace std;
const int MAXN=1e6+5;
int cover[MAXN<<2];
int sum[MAXN<<2];
inline int read(){//快读
    char ch=getchar();int x=0,f=1;
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
void up(int rt){//更新本节点
    sum[rt] = sum[lch(rt)] + sum[rch(rt)];
}

void down(int rt, int l, int r){
    if(cover[rt]){
        cover[lch(rt)] ^= 1;
        cover[rch(rt)] ^= 1;
        int m = (l + r) >> 1;
        sum[lch(rt)] = m - l + 1 - sum[lch(rt)];
        sum[rch(rt)] = r - m - sum[rch(rt)];
        cover[rt] = 0;
    }
}
void update(int L, int R, int l, int r, int rt){//更新
    if(L <= l && R >= r){
        cover[rt] ^= 1;
        sum[rt] = r - l + 1 - sum[rt];
        return;
    }
    down(rt, l, r);
    int m = (l + r) >> 1;
    if(L <= m) update(L, R, lson);
    if(R > m) update(L, R, rson);
    up(rt);
}

int query(int L, int R, int l, int r, int rt){
    if(L <= l && R >= r) return sum[rt];
    down(rt, l, r);
    int m = (l + r) >> 1;
    int ret = 0;
    if(L <= m) ret += query(L, R, lson);
    if(R > m) ret += query(L, R, rson);
    return ret;
}
int main(){
    int x;
    x=read();
    int n,m;
    for(int k=1;k<=x;k++){
        memset(cover,0,sizeof(cover));
        memset(sum,0,sizeof(sum));
        n=read(),m=read();
        for(int i=0;i<m;i++){
            int s,t;//更新区间[s,t]
            s=read(),t=read();
            update(s,t,1,n,1);
        }
        printf("Case #%d: ",k);
        printf("%d\n",query(1,n,1,n,1));
        //printf("%d\n",sum[1]);
    }
    return 0;
}