feat: leetcode 940

Author: deweyou

README.md

@@ -2,7 +2,7 @@
 
 <p align="center">
 <!-- TOPICS COUNT START -->
-<img src="https://img.shields.io/badge/-进度:519-green" alt="进度:519">
+<img src="https://img.shields.io/badge/-进度:520-green" alt="进度:520">
 <!-- TOPICS COUNT END -->
 <a href="./assets/docs/TOPICS.md"><img src="https://img.shields.io/badge/-题库目录-blue" alt="题库目录"></a>
 <a href="./assets/docs/CATEGORIES.md"><img src="https://img.shields.io/badge/-题库分类-red" alt="题库分类"></a>

assets/data/categories.json

@@ -1639,6 +1639,12 @@
         "path": "./problemset/flip-string-to-monotone-increasing/README.md",
         "difficulty": "中等"
       },
+      {
+        "id": "940",
+        "title": "不同的子序列 II",
+        "path": "./problemset/distinct-subsequences-2/README.md",
+        "difficulty": "困难"
+      },
       {
         "id": "1800",
         "title": "最大升序子数组和",

assets/data/topics.json

@@ -4149,6 +4149,16 @@
     "url": "https://leetcode-cn.com/problems/reorder-data-in-log-files/",
     "path": "./problemset/reorder-data-in-log-files/README.md"
   },
+  {
+    "id": "940",
+    "title": {
+      "cn": "不同的子序列 II",
+      "en": "distinct-subsequences-2"
+    },
+    "difficulty": "困难",
+    "url": "https://leetcode.cn/problems/distinct-subsequences-ii/",
+    "path": "./problemset/distinct-subsequences-2/README.md"
+  },
   {
     "id": "942",
     "title": {

assets/docs/CATEGORIES.md

@@ -306,6 +306,7 @@
 | 871. [最低加油次数](../../problemset/minimum-number-of-refueling-stops/README.md) | 困难 |
 | 873. [最长的斐波那契子序列的长度](../../problemset/length-of-longest-fibonacci-subsequence/README.md) | 中等 |
 | 926. [将字符串翻转到单调递增](../../problemset/flip-string-to-monotone-increasing/README.md) | 中等 |
+| 940. [不同的子序列 II](../../problemset/distinct-subsequences-2/README.md) | 困难 |
 | 1800. [最大升序子数组和](../../problemset/maximum-ascending-subarray-sum/README.md) | 简单 |
 | 1994. [好子集的数目](../../problemset/the-number-of-good-subsets/README.md) | 困难 |
 | 2100. [适合打劫银行的日子](../../problemset/find-good-days-to-rob-the-bank/README.md) | 中等 |

assets/docs/TOPICS.md

@@ -830,6 +830,8 @@
 
 [937. 重新排列日志文件](../../problemset/reorder-data-in-log-files/README.md)
 
+[940. 不同的子序列 II](../../problemset/distinct-subsequences-2/README.md)
+
 [942. 增减字符串匹配](../../problemset/di-string-match/README.md)
 
 [944. 删列造序](../../problemset/delete-columns-to-make-sorted/README.md)

problemset/distinct-subsequences-2/README.md

@@ -0,0 +1,62 @@
+# 不同的子序列 II
+
+> 难度：困难
+>
+> https://leetcode.cn/problems/distinct-subsequences-ii/
+
+## 题目
+
+给定一个字符串 `s`，计算 `s` 的 **不同非空子序列** 的个数。因为结果可能很大，所以返回答案需要对 `10^9 + 7` 取余 。
+
+字符串的 **子序列** 是经由原字符串删除一些（也可能不删除）字符但不改变剩余字符相对位置的一个新字符串。
+
+- 例如，`"ace"` 是 `"abcde"` 的一个子序列，但 `"aec"` 不是。
+ 
+### 示例
+
+#### 示例 1：
+
+```
+输入：s = "abc"
+输出：7
+解释：7 个不同的子序列分别是 "a", "b", "c", "ab", "ac", "bc", 以及 "abc"。
+```
+
+#### 示例 2：
+
+```
+输入：s = "aba"
+输出：6
+解释：6 个不同的子序列分别是 "a", "b", "ab", "ba", "aa" 以及 "aba"。
+```
+
+#### 示例 3：
+
+```
+输入：s = "aaa"
+输出：3
+解释：3 个不同的子序列分别是 "a", "aa" 以及 "aaa"。
+```
+
+## 解题
+
+```ts 
+/**
+ * 动态规划
+ * @desc 时间复杂度 O(N+|Σ|)  空间复杂度 O(|Σ|)
+ * @param s
+ * @returns
+ */
+export function distinctSubseqII(s: string): number {
+  const MOD = 1000000007
+  const g = new Array(26).fill(0)
+  const n = s.length; let total = 0
+  for (let i = 0; i < n; ++i) {
+    const oi = s[i].charCodeAt(0) - 'a'.charCodeAt(0)
+    const prev = g[oi]
+    g[oi] = (total + 1) % MOD
+    total = ((total + g[oi] - prev) % MOD + MOD) % MOD
+  }
+  return total
+}
+```

problemset/distinct-subsequences-2/index.spec.ts

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+import { describe, expect, it } from 'vitest'
+import { distinctSubseqII } from '.'
+
+describe('不同的子序列 II', () => {
+  testCase(distinctSubseqII)
+})
+
+function testCase(fn: typeof distinctSubseqII) {
+  it.each([
+    ['abc', 7],
+    ['aba', 6],
+    ['aaa', 3],
+  ])('示例%#', (s, expected) => {
+    expect(fn(s)).toBe(expected)
+  })
+}

problemset/distinct-subsequences-2/index.ts

@@ -0,0 +1,18 @@
+/**
+ * 动态规划
+ * @desc 时间复杂度 O(N+|Σ|)  空间复杂度 O(|Σ|)
+ * @param s
+ * @returns
+ */
+export function distinctSubseqII(s: string): number {
+  const MOD = 1000000007
+  const g = new Array(26).fill(0)
+  const n = s.length; let total = 0
+  for (let i = 0; i < n; ++i) {
+    const oi = s[i].charCodeAt(0) - 'a'.charCodeAt(0)
+    const prev = g[oi]
+    g[oi] = (total + 1) % MOD
+    total = ((total + g[oi] - prev) % MOD + MOD) % MOD
+  }
+  return total
+}