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什么是线段树

struct node{   	int l;//左区间端点 	int r;//右区间端点 	int val;//此节点存值 	int len;//子结点管理区间长度 }tree[1005];

建树

void build(int cur, int l, int r){   	int mid=(l+r)/2;	tree[cur].l=l, tree[cur].r=r;	tree[cur].val=0, tree[cur].len=r-l+1;	if (l==r)//只有到达叶结点时才把数组的值赋给它 		tree[cur].val=arr[l];//arr为输入数据的数组	else{   		build(cur*2, l, mid);		build(cur*2+1, mid+1, r);		tree[cur].val=tree[cur*2].val+tree[cur*2+1].val;//回溯过程中更新父结点 	}}

单点更新

void updata(int cur, int id, int val)//cur为节点编号，id为修改数据的编号，val为增加的值 {   	int l=tree[cur].l, r=tree[cur].r;	int mid=(l+r)/2;	if (l==r){   		tree[cur].val+=val;		return;	}	if (id<=mid)		updata(cur*2, id, val);	else		updata(cur*2+1, id, val);	tree[cur].val=tree[cur*2].val+tree[cur*2+1].val;//回溯过程中更新父结点 }

区间查询

int query(int cur, int ql, int qr){   	int l=tree[cur].l, r=tree[cur].r;	int mid=(l+r)/2, res=0;	if (ql<=l && r<=qr)//如果此节点的区间在查询区间内，直接返回 		return tree[cur].val;	if (ql<=mid)		res+=query(cur*2, ql, qr);	if (qr>mid)//注意这里是两个if，不是分支关系 		res+=query(cur*2+1, ql, qr);	return res;}

完整模板

#include 
   
    #include 
    
     #include 
     
      using namespace std;struct node{   	int l;	int r;	int val;	int len;	int lazy;}tree [505];int arr[505];void pushup(int cur){   	tree[cur].val=tree[cur*2].val+tree[cur*2+1].val;}void pushdown(int cur){   	if (tree[cur].lazy!=0){   		tree[cur*2].lazy+=tree[cur].lazy;		tree[cur*2+1].lazy+=tree[cur].lazy;		tree[cur*2].val+=tree[cur*2].len*tree[cur].lazy;		tree[cur*2+1].val+=tree[cur*2+1].len*tree[cur].lazy;		tree[cur].lazy=0;	}}//建树 void build(int cur, int l, int r){   	int mid=(l+r)/2;	tree[cur].l=l, tree[cur].r=r;	tree[cur].val=0, tree[cur].len=r-l+1;	tree[cur].lazy=0;	if (l==r)		tree[cur].val=arr[l];	else{   		build(cur*2, l, mid);		build(cur*2+1, mid+1, r);		pushup(cur);	}}//单点更新  加值 void update_point(int cur, int pos, int val)//cur为节点编号，id为修改数据的编号，val为增加的值 {   	int l=tree[cur].l, r=tree[cur].r;	int mid=(l+r)/2;	if (l==r){   		tree[cur].val+=val;		tree[cur].lazy+=val;		return;	}	if (pos<=mid)		update_point(cur*2, pos, val);	else		update_point(cur*2+1, pos, val);	pushup(cur);} //单点查询int query_point(int cur, int pos){   	if (tree[cur].l==tree[cur].r)		return tree[cur].val;	pushdown(cur);		int mid=(tree[cur].l+tree[cur].r)/2;	if (pos
      
       mid)		ans+=query_interval(cur*2+1, ql, qr);	return ans; } //区间更新 加值 void update_interval(int cur, int l, int r, int val){   	if (l<=tree[cur].l && tree[cur].r<=r){   		tree[cur].val+=(tree[cur].r-tree[cur].l+1)*val;		tree[cur].lazy+=val;		return;	}	pushdown(cur);		int mid=(tree[cur].l+tree[cur].r)/2;	if (l<=mid)		update_interval(cur*2, l, r, val);	if (r>mid)		update_interval(cur*2+1, l, r, val);		pushup(cur);} int main(){   		return 0;}
      
     
    
   

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