https://leetcode.cn/problems/shu-zu-zhong-de-ni-xu-dui-lcof/

Author: masx200

README.md

@@ -10,6 +10,8 @@ leetcode 测试
 
 ##### 包含的内容如下
 
+https://leetcode.cn/problems/shu-zu-zhong-de-ni-xu-dui-lcof/
+
 https://leetcode.cn/problems/rank-from-stream-lcci/
 
 https://leetcode.cn/problems/minimum-cost-to-hire-k-workers/

rank-from-stream-lcci/index.ts

@@ -1,9 +1,9 @@
 export default class StreamRank {
-    #bit = new BinaryIndexTree(50002);
+    #bit = new BinaryIndexTree(50001);
     constructor() {}
 
     track(x: number): void {
-        this.#bit.change(x + 1, 1);
+        this.#bit.update(x + 1, 1);
     }
 
     getRankOfNumber(x: number): number {
@@ -16,10 +16,10 @@ export class BinaryIndexTree {
     }
     #tree: number[];
     constructor(public size: number) {
-        this.#tree = Array(size).fill(0);
+        this.#tree = Array(size+1).fill(0);
     }
-    change(i: number, x: number) {
-        for (let p = i; p < this.size; p += BinaryIndexTree.lowbit(p)) {
+    update(i: number, x: number) {
+        for (let p = i; p <= this.size; p += BinaryIndexTree.lowbit(p)) {
             this.#tree[p] += x;
         }
     }

shu-zu-zhong-de-ni-xu-dui-lcof/index.ts

@@ -0,0 +1,17 @@
+import { BinaryIndexTree } from "../rank-from-stream-lcci/index.ts";
+import { le as binarySearch } from "https://esm.sh/@masx200/[email protected]";
+export default function reversePairs(nums: number[]): number {
+    const n = nums.length;
+    const tmp = Array.from(nums);
+    tmp.sort((a, b) => a - b);
+    for (let i = 0; i < n; ++i) {
+        nums[i] = binarySearch(tmp, nums[i]) + 1;
+    }
+    const bit = new BinaryIndexTree(n);
+    let ans = 0;
+    for (let i = n - 1; i >= 0; i--) {
+        ans += bit.query(nums[i] - 1);
+        bit.update(nums[i], 1);
+    }
+    return ans;
+}