线段树

#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <set>
#include <queue>
#include <map>
#include <sstream>
#include <cstdio>
#include <cstring>
#include <numeric>
#include <cmath>
#include <iomanip>
#include <deque>
#include <bitset>
//#include <unordered_set>
//#include <unordered_map>
//#include <bits/stdc++.h>
//#include <xfunctional>
#define ll  long long
#define PII  pair<int, int>
using namespace std;
int dir[5][2] = { { 0,1 } ,{ 0,-1 },{ 1,0 },{ -1,0 } ,{ 0,0 } };
const long long INF = 0x7f7f7f7f7f7f7f7f;
const int inf = 0x3f3f3f3f;
const double pi = 3.14159265358979;
const int mod = 1e9 + 7;
const int N = 2e5+5;
//if(x<0 || x>=r || y<0 || y>=c)
//1000000000000000000

inline ll read()
{
    ll x = 0; bool f = true; char c = getchar();
    while (c < '0' || c > '9') { if (c == '-') f = false; c = getchar(); }
    while (c >= '0' && c <= '9') x = (x << 1) + (x << 3) + (c ^ 48), c = getchar();
    return f ? x : -x;
}

int A[100000] = { 0,1,2,3,4,5,6 };

int tree[N];

void build(int node, int start, int end)
{
    if (start == end)
    {
        // Leaf node will have a single element
        tree[node] = A[start];
    }
    else
    {
        int mid = (start + end) / 2;
        // Recurse on the left child
        build(2 * node, start, mid);
        // Recurse on the right child
        build(2 * node + 1, mid + 1, end);
        // Internal node will have the sum of both of its children
        tree[node] = tree[2 * node] + tree[2 * node + 1];
    }
}

void update(int node, int start, int end, int idx, int val)
{
    if (start == end)
    {
        // Leaf node
        A[idx] += val;
        tree[node] += val;
    }
    else
    {
        int mid = (start + end) / 2;
        if (start <= idx && idx <= mid)
        {
            // If idx is in the left child, recurse on the left child
            update(2 * node, start, mid, idx, val);
        }
        else
        {
            // if idx is in the right child, recurse on the right child
            update(2 * node + 1, mid + 1, end, idx, val);
        }
        // Internal node will have the sum of both of its children
        tree[node] = tree[2 * node] + tree[2 * node + 1];
    }
}
int query(int node, int start, int end, int l, int r)
{
    if (r < start || end < l)
    {
        // range represented by a node is completely outside the given range
        return 0;
    }
    if (l <= start && end <= r)
    {
        // range represented by a node is completely inside the given range
        return tree[node];
    }
    // range represented by a node is partially inside and partially outside the given range
    int mid = (start + end) / 2;
    int p1 = query(2 * node, start, mid, l, r);
    int p2 = query(2 * node + 1, mid + 1, end, l, r);
    return (p1 + p2);
}
int main()
{
    int size = 6;
    build(1, 1, size);
    int res=query(1, 1, size, 2, 3);
    cout << res<<endl;
    return 0;
}