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TangDou/AcWing/BIT/P3374.md

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+## [$P3374$ 【模板】树状数组 1](https://www.luogu.com.cn/problem/P3374)
+
+```cpp {.line-numbers}
+#include <bits/stdc++.h>
+
+using namespace std;
+typedef long long LL;
+const int N = 5 * 1e5 + 10;
+int n, m;
+int a[N];
+
+// 树状数组模板
+// 用while循环优于for循环，因为没有i变量，不易写错，代码更短
+#define lowbit(x) (x & -x)
+int c[N];
+void add(int x, int v) {
+    while (x < N) c[x] += v, x += lowbit(x);
+}
+LL sum(int x) {
+    LL res = 0;
+    while (x) res += c[x], x -= lowbit(x);
+    return res;
+}
+
+int main() {
+    cin >> n >> m;
+    for (int i = 1; i <= n; i++)
+        cin >> a[i], add(i, a[i]); // 维护进入树状数组，两个概念：位置，值
+
+    while (m--) {
+        int op, x, y;
+        cin >> op >> x >> y;
+        if (op == 1)
+            add(x, y); // 在x位置上加上y
+        else
+            // 计算[x,y]之间的数字和
+            cout << sum(y) - sum(x - 1) << endl;
+    }
+    return 0;
+}
+```