$b_i$ 为原序列 $a_i$ 的差分序列,则
$$
b_i=
\begin{cases}
a_i - a_{i-1} && i \in [2, n] \\\
a_1 && i = 1
\end{cases}
$$
差分序列的前缀和等于原序列
$$
a_i = \sum_{j = 1}^{i} b_j
$$
根据差分序列的性质,我们用树状数组维护差分序列
- 初始化树状数组,$\textbf{tr}[i] = A[i] - A[i-1]$
$\textbf{add}(i, A_i-A_{i-1})$ - 区间 $[l, r] + d$ (区间内所有的数都加 $d$)
$\textbf{add}(l, d), \textbf{add}(r+1, -d)$ - 询问修改后下标为 $x$ 的值,执行
$\textbf{sum}(x)$
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>
#include <queue>
#include <vector>
#include <stack>
#include <map>
#include <set>
#include <sstream>
#include <iomanip>
#include <cmath>
#include <bitset>
#include <assert.h>
#include <unordered_map>
using namespace std;
typedef long long ll;
#define Cmp(a, b) memcmp(a, b, sizeof(b))
#define Cpy(a, b) memcpy(a, b, sizeof(b))
#define Set(a, v) memset(a, v, sizeof(a))
#define debug(x) cout << #x << ": " << x << endl
#define _forS(i, l, r) for(set<int>::iterator i = (l); i != (r); i++)
#define _rep(i, l, r) for(int i = (l); i <= (r); i++)
#define _for(i, l, r) for(int i = (l); i < (r); i++)
#define _forDown(i, l, r) for(int i = (l); i >= r; i--)
#define debug_(ch, i) printf(#ch"[%d]: %d\n", i, ch[i])
#define debug_m(mp, p) printf(#mp"[%d]: %d\n", p->first, p->second)
#define debugS(str) cout << "dbg: " << str << endl;
#define debugArr(arr, x, y) _for(i, 0, x) { _for(j, 0, y) printf("%c", arr[i][j]); printf("\n"); }
#define _forPlus(i, l, d, r) for(int i = (l); i + d < (r); i++)
#define lowbit(i) (i & (-i))
#define MPR(a, b) make_pair(a, b)
pair<int, int> crack(int n) {
int st = sqrt(n);
int fac = n / st;
while (n % st) {
st += 1;
fac = n / st;
}
return make_pair(st, fac);
}
inline ll qpow(ll a, int n) {
ll ans = 1;
for(; n; n >>= 1) {
if(n & 1) ans *= 1ll * a;
a *= a;
}
return ans;
}
template <class T>
inline bool chmax(T& a, T b) {
if(a < b) {
a = b;
return true;
}
return false;
}
ll gcd(ll a, ll b) {
return b == 0 ? a : gcd(b, a % b);
}
ll ksc(ll a, ll b, ll mod) {
ll ans = 0;
for(; b; b >>= 1) {
if (b & 1) ans = (ans + a) % mod;
a = (a * 2) % mod;
}
return ans;
}
ll ksm(ll a, ll b, ll mod) {
ll ans = 1 % mod;
a %= mod;
for(; b; b >>= 1) {
if (b & 1) ans = ksc(ans, a, mod);
a = ksc(a, a, mod);
}
return ans;
}
template <class T>
inline bool chmin(T& a, T b) {
if(a > b) {
a = b;
return true;
}
return false;
}
template<class T>
bool lexSmaller(vector<T> a, vector<T> b) {
int n = a.size(), m = b.size();
int i;
for(i = 0; i < n && i < m; i++) {
if (a[i] < b[i]) return true;
else if (b[i] < a[i]) return false;
}
return (i == n && i < m);
}
// ============================================================== //
const int maxn = 100000 + 10;
ll a[maxn], tr[maxn];
int n, m;
void add(int x, int d) {
for (int i = x; i <= n; i += lowbit(i)) tr[i] += d;
}
ll sum(int x) {
ll ans = 0;
for (int i = x; i; i -= lowbit(i)) ans += tr[i];
return ans;
}
int main() {
freopen("input.txt", "r", stdin);
scanf("%d%d", &n, &m);
for (int i = 1; i <= n; i++) scanf("%lld", &a[i]);
// prework
for (int i = 1; i <= n; i++) add(i, a[i]-a[i-1]);
// solve
while (m--) {
char cmd[2];
scanf("%s", cmd);
if (cmd[0] == 'Q') {
int x;
scanf("%d", &x);
printf("%lld\n", sum(x));
}
else {
int l, r, d;
scanf("%d%d%d", &l, &r, &d);
add(l, d), add(r+1, -d);
}
}
}