python/TangDou/AcWing/BIT/P3368_2.cpp

#include <bits/stdc++.h>
using namespace std;

const int N = 5e5 + 10;
int a[N]; // a是原数组。c是差分数组，用树状数组维护

int n, m;
// 树状数组模板
typedef long long LL;
#define lowbit(x) (x & -x)
int c[N];
void add(int x, int d) {
    for (int i = x; i < N; i += lowbit(i)) c[i] += d;
}
LL sum(int x) {
    LL res = 0;
    for (int i = x; i; i -= lowbit(i)) res += c[i];
    return res;
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("P3368.in", "r", stdin);
#endif
    scanf("%d %d", &n, &m);

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

    // 保存差分数组
    for (int i = 1; i <= n; i++) add(i, a[i] - a[i - 1]);

    int op, l, r, v, k;
    while (m--) {
        scanf("%d", &op);
        if (op == 1) {
            scanf("%d %d %d", &l, &r, &v);
            add(l, v), add(r + 1, -v);
        } else {
            scanf("%d", &k);
            // 树状数组维护的是变化量，还需要加上原来的值
            printf("%d\n", sum(k)); // 求某点的值
        }
    }

    return 0;
}