線段樹的基本知識可以先google一下，不是很難理解

線段樹功能:update:單點增減 query:區間求和

#include <bits/stdc++.h>
#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
using namespace std;

const int MAXN = 50008;
int sum[MAXN<<2];

void build(int l, int r, int rt)
{
    if(l == r)
    {
        scanf(
 
"%d", &sum[rt]);
        return;
    }
    int m = (l + r) >> 1;
    build(lson);
    build(rson);
    sum[rt] = sum[rt<<1] + sum[rt<<1|1];
}

int query(int L, int R, int l, int r, int rt)
{
    if(L <= l && r <= R) return sum[rt];
    int ret = 0;
    
 
int m = (l + r) >> 1;
    if(L <= m) ret += query(L, R, lson);
    if(R > m) ret += query(L, R, rson);
    return ret;
}

void updata(int p, int add, int l, int r, int rt)
{
    if(l == r)
    {
        sum[rt] += add;
        return;
    }
    int m = (l + r) >> 1;
    
 
if(p <= m) updata(p, add, lson);
    else updata(p, add, rson);
    sum[rt] = sum[rt<<1] + sum[rt<<1|1];
}

int main()
{
//    freopen("in.txt", "r", stdin);
    int T, Case = 0;
    scanf("%d", &T);
    while(T--)
    {
        int n;
        scanf("%d", &n);
        build(1, n, 1);
        printf("Case %d:\n", ++Case);
        char s[10];
        while(~scanf("%s", s))
        {
            if(s[0] == ‘E‘) break;
            int a,b;
            scanf("%d%d", &a, &b);
            if(s[0] == ‘Q‘) printf("%d\n", query(a, b, 1, n, 1));
            else if(s[0] == ‘A‘) updata(a, b, 1, n, 1);
            else updata(a, -b, 1, n, 1);
        }
    }
    return 0;
}

hdu 1116 敵兵布陣 線段樹 區間求和 單點更新