hdu 1166 敌兵布阵【线段树】（求给定区间和）

#include <cstdio>
#include <iostream>
#include <cstring>
#include <string>
using namespace std;
const int MAXN = 50000 + 100;
int n,a[MAXN];

struct tree
{
    int l, r;
    int s;
}trees[MAXN * 4];


void buildtree(int rs, int l, int r)
{
    trees[rs].l = l;
    trees[rs].r = r;
    if (trees[rs].l == trees[rs].r)
    {
        trees[rs].s = a[l];
        return;
    }
    int mid = (trees[rs].l + trees[rs].r) / 2;
    buildtree(rs * 2, trees[rs].l, mid);
    buildtree(rs * 2 + 1, mid + 1, trees[rs].r);                  //rs*2+1也可表示为 rs<<1|1
    trees[rs].s = trees[rs * 2].s + trees[rs * 2 + 1].s;
}

void update(int rs, int ord, int goal)
{
    if (trees[rs].l == ord && trees[rs].r == ord)
    {
        trees[rs].s = goal;
        return;
    }
    int mid = (trees[rs].l + trees[rs].r) / 2;
    if (ord <= mid)update(rs * 2, ord, goal);
    else if (ord > mid)update(rs * 2 + 1, ord, goal);
    trees[rs].s = trees[rs * 2].s + trees[rs * 2 + 1].s;
}

int querry(int rs, int l, int r)
{
    if (trees[rs].l == l && trees[rs].r == r)
    {
        return trees[rs].s;
    }
    int mid = (trees[rs].l + trees[rs].r) / 2;
    if (r <= mid)return querry(rs * 2, l, r);
    else if (l > mid)return querry(rs * 2 + 1, l, r);
    else if(l<=mid && r>mid)
    {
        return querry(rs * 2, l, mid) + querry(rs * 2 + 1, mid + 1, r);
    }
    return 0;
}


int main()
{
    int t; cin >> t;
    int ans = 0;
    while (t--)
    {    
        
        cin >> n;
        memset(a, 0, sizeof(a));
        memset(trees, 0, sizeof(trees));
        for (int i = 1; i <= n; i++)
            scanf("%d", &a[i]);
        buildtree(1, 1, n);
        printf("Case %d:\n", ++ans);
        string str;
        while (cin >> str)
        {
            if (str == "End")break;
            if (str == "Query")
            {
                int ac, bc;
                scanf("%d %d", &ac, &bc);
                printf("%d\n",querry(1, ac, bc));
            }
            else if (str == "Add")
            {
                int ac, bc;
                scanf("%d %d", &ac, &bc);
                int res = a[ac] + bc;
                update(1, ac, res);
            }
            else if(str=="Sub")
            {
                int ac, bc;
                scanf("%d %d", &ac, &bc);
                int res = a[ac] - bc;
                update(1, ac, res);
            }
        }
    }
    return 0;
}