upd:更新树状数组模板

Author: deeper-coder

数据结构/树状数组/树状数组.py

@@ -1,29 +1,33 @@
-class FenwickTree:
-    def __init__(self, n):
-        self.size = n
-        self.tree = [0] * (n + 1)
+class Fenwick:
+    __slots__ = "f"
 
-    # 将下标 i 上的数加一
-    def inc(self, i: int) -> None:
-        while i < len(self.tree):
-            self.tree[i] += 1
+    def __init__(self, n: int):
+        self.f = [0] * (n + 1)
+
+    # 将下标i处值增加val
+    def update(self, i: int, val: int) -> None:
+        while i < len(self.f):
+            self.f[i] += val
             i += i & -i
 
     # 返回闭区间 [1, i] 的元素和
-    def sum(self, i: int) -> int:
+    def pre(self, i: int) -> int:
         res = 0
         while i > 0:
-            res += self.tree[i]
+            res += self.f[i]
             i &= i - 1
         return res
 
-    # 返回闭区间 [left, right] 的元素和
-    def query(self, left: int, right: int) -> int:
-        return self.sum(right) - self.sum(left - 1)
+    # 返回闭区间 [l, r] 的元素和
+    def query(self, l: int, r: int) -> int:
+        if r < l:
+            return 0
+        return self.pre(r) - self.pre(l - 1)
+
 
 n = II()
 a = LII()
 num2idx = {}
-for i, x in enumerate(sorted(a), start=1):
+for i, x in enumerate(sorted(a), 1):
     num2idx[x] = i
-ft = FenwickTree(n)
+f = Fenwick(n)