HDU1166敌兵布阵 分块解法，分块练习

题目链接： http://acm.hdu.edu.cn/showproblem.php?pid=1166

线段树，树状数组的模板题。用来入门分块。

#include
using namespace std;
const int N = 5e4+10;

int block;
int n;
int arr[N], sum[N];


void update(int pos, int val){
    arr[pos] += val;
    sum[pos/block] += val;
}

int query(int s, int e){
    int ans = 0;
    for (int i = 0, l = 1, r = block-1; i <= n/block; i++, l = i*block, r += block){
        int L = max(l, s);
        int R = min(r, e);
        if (L > R) continue;
        if (L == l && R == r) ans += sum[i];
        else for (int j = L; j <= R; j++)
            ans += arr[j];
    }
    return ans;
}

int main(){
    int T;
    scanf("%d", &T);
    for (int kase = 1; kase <= T; kase++){
        memset(sum, 0, sizeof(sum));
        scanf("%d", &n);
        block = (int)sqrt(n);

        for (int i = 1; i <= n; i++){
            scanf("%d", &arr[i]);
            sum[i/block] += arr[i];
        }

        printf("Case %d:\n", kase);
        char opt[10];
        while(scanf("%s", opt) == 1){
            if (opt[0] == 'E') break;
            if (opt[0] == 'Q'){
                int s, e;
                scanf("%d%d", &s, &e);
                printf("%d\n", query(s, e));
            }
            else{
                int pos, val;
                scanf("%d %d", &pos, &val);
                if (opt[0] == 'A') update(pos, val);
                else update(pos, -val);
            }
        }
    }
    return 0;
}