hdu 1166 敌兵布阵

这题用了自顶向下的递归方式。

#include <iostream>
#include <cstring>
using namespace std;
const int MAXD = 50005;
int tree[4*MAXD];
int a[MAXD],D;
int query(int x,int y)
{
    int i=D+x-1, j=D+y+1, ans=0;
    for(; i+1 != j; i>>=1,j>>=1)
    {
        if(~i & 1)
            ans += tree[i^1];
        if(j & 1)
            ans += tree[j^1];
    }
    return ans;
}
void update(int n)
{
    for(; n ^ 1; n >>= 1)
        tree[n>>1] = tree[n]+tree[n^1];
}
int main()
{
    int T,n,m,i,x,y;
    char cmd[7];
    cin>>T;
    m = 1;
    while(T--)
    {
        cin>>n;
        for(i = 1; i <= n; i++)
            cin>>a[i];
        D = 1;
        while(D < n+2)
            D <<= 1;
        memset(tree,0,sizeof(tree));
        for(i = 1; i <= n; i++)
            tree[D+i] = a[i];
        for(i = D-1; i; i--)
            tree[i] = tree[i<<1] + tree[i<<1|1];
        cout<<"Case "<<m++<<":\n";
        cin>>cmd;
        while(cmd[0] != 'E')
        {
            cin>>x>>y;
            if(cmd[0] == 'Q')
                cout<<query(x,y)<<endl;
            else if(cmd[0] == 'A')
            {
                tree[D+x] += y;
                update(D+x);
            }
            else if(cmd[0] == 'S')
            {
                tree[D+x] -= y;
                update(D+x);
            }
            cin>>cmd;
        }
    }
    return 0;
}