Luo Gu p1047 segment tree tree outside the school practice

Very easy,

Note that it is to start at both ends, that is the position 0 is also like a tree

Because I too weak, a red question to pay 4,5 times

Due to cut down the tree is gone, lazy biggest mark is 1;

Directly attached to the bar code

#include<bits/stdc++.h>

using namespace std;

inline int read(){int s=0,w=1;char ch=getchar();while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=getchar();}while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();return s*w;}
inline void write(int x) {if(x<0) putchar('-'),x=-x; if(x>9) write(x/10); putchar(x%10+'0'); }

int sum[400010],lazy[400010];

void build(int root,int l,int r){
    if(l == r){
        sum[root] = 1;
        return ;
    }
    int mid = (l + r) >> 1;
    int left = root << 1;
    int right = left + 1;
    build(left,l,mid);
    build(right,mid + 1,r);
    sum[root] = sum[left] + sum[right];
}

void add(int root,int l,int r,int k){
    if(k == 0)
        return ;
    if(lazy[root])
        return ;
    lazy[root] = 1;
    sum[root] = 0;
    return ;
}

void putdown(int root,int l,int r){
    if(lazy[root] == 0)
        return ;
    int mod = lazy[root] % 2; int mid = (l + r) >> 1;
    add(root * 2,l,mid,mod);
    add(root * 2 + 1,mid + 1,r,mod);
    lazy[root] = 0;
    return ;
}

void change(int root,int l,int r,int x,int y){
    if(l > y || r < x)
        return ;
    if(l >= x && r <= y){
        add(root,l,r,1);
        return ;
    }
    int mid = (l + r) >> 1;
    putdown(root,l,r);
    int left = root << 1;
    int right = left + 1;
    if(x <= mid) change(left,l,mid,x,y);
    if(mid < y) change(right,mid + 1,r,x,y);
    sum[root] = sum[left] + sum[right];
}

int find(int root,int l,int r,int x,int y){
    if(l >= x && r <= y){
        return sum[root];
    }
    int mid = (l + r) >> 1,ans = 0;
    int left = root << 1;
    int right = left + 1;
    putdown(root,l,r);
    if(x <= mid) ans += find(left,l,mid,x,y);
    if(mid < y) ans += find(right,mid + 1,r,x,y);
    return ans;
}

int main(){
    int n,m;
    cin >> n >> m;
    build(1,1,n + 1);
    for(int i = 1; i <= m;++i){
        int y,z;
        scanf("%d%d",&y,&z);
        change(1,1,n + 1,y + 1,z + 1);
    }
    write(find(1,1,n + 1,1,n + 1));
    cout<<endl;
    return 0;
}