acwing 242. 一个简单的整数问题

输入样例：

10 5
1 2 3 4 5 6 7 8 9 10
Q 4
Q 1
Q 2
C 1 6 3
Q 2

输出样例：

4
1
2
5

#include <iostream>
#include <vector>
#include <algorithm>


using namespace std;

const int N = 100010;

typedef long long ll;
typedef long long LL;

int n, m;
int a[N];
ll tr[N];

int lowbit(int x) {
    return x & -x;
}

void add(int x, int c)
{
    for (int i = x; i <= n; i += lowbit(i)) tr[i] += c;
}


ll sum(int x)
{
    ll res = 0;
    for (int i = x; i; i -= lowbit(i)) res += tr[i];
    return res;
}


int main()
{
    scanf("%d %d", &n, &m);

    for (int i = 1; i <= n; i++) scanf("%d", &a[i]);

    for (int i = 1; i <= n; i++) add(i, a[i] - a[i - 1]);

    while (m--) {
        char op[2];
        int l, r, d;
        scanf("%s%d",op,&l);

        if (*op == ‘C‘) {
            scanf("%d%d", &r, &d);
            add(l, d); add(r + 1, -d);
        }
        else {
            printf("%lld\n",sum(l));
        }
    }

    return 0;
}