+ problem 940

Author: fruit-in

Problemset/0940-Distinct Subsequences II/README.md

@@ -0,0 +1,51 @@
+# 940. Distinct Subsequences II
+Given a string s, return *the number of **distinct non-empty subsequences** of* `s`. Since the answer may be very large, return it **modulo** <code>10<sup>9</sup> + 7</code>.
+
+A **subsequence** of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., `"ace"` is a subsequence of `"abcde"` while `"aec"` is not.
+
+#### Example 1:
+<pre>
+<strong>Input:</strong> s = "abc"
+<strong>Output:</strong> 7
+<strong>Explanation:</strong> The 7 distinct subsequences are "a", "b", "c", "ab", "ac", "bc", and "abc".
+</pre>
+
+#### Example 2:
+<pre>
+<strong>Input:</strong> s = "aba"
+<strong>Output:</strong> 6
+<strong>Explanation:</strong> The 6 distinct subsequences are "a", "b", "ab", "aa", "ba", and "aba".
+</pre>
+
+#### Example 3:
+<pre>
+<strong>Input:</strong> s = "aaa"
+<strong>Output:</strong> 3
+<strong>Explanation:</strong> The 3 distinct subsequences are "a", "aa" and "aaa".
+</pre>
+
+#### Constraints:
+* `1 <= s.length <= 2000`
+* `s` consists of lowercase English letters.
+
+## Solutions (Rust)
+
+### 1. Solution
+```Rust
+impl Solution {
+ pub fn distinct_subseq_ii(s: String) -> i32 {
+ const MOD: i32 = 1_000_000_007;
+ let n = s.len();
+ let mut last_index = [n; 26];
+ let mut dp = vec![0_i32; n + 1];
+ dp[n] = -1;
+
+ for (i, c) in s.bytes().map(|c| (c - b'a') as usize).enumerate() {
+ dp[i + 1] = (dp[i] * 2 - dp[last_index[c]]).rem_euclid(MOD);
+ last_index[c] = i;
+ }
+
+ *dp.last().unwrap()
+ }
+}
+```

Problemset/0940-Distinct Subsequences II/README_CN.md

@@ -0,0 +1,53 @@
+# 940. 不同的子序列 II
+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 1:
+<pre>
+<strong>输入:</strong> s = "abc"
+<strong>输出:</strong> 7
+<strong>解释:</strong> 7 个不同的子序列分别是 "a", "b", "c", "ab", "ac", "bc", 以及 "abc"。
+</pre>
+
+#### 示例 2:
+<pre>
+<strong>输入:</strong> s = "aba"
+<strong>输出:</strong> 6
+<strong>解释:</strong> 6 个不同的子序列分别是 "a", "b", "ab", "ba", "aa" 以及 "aba"。
+</pre>
+
+#### 示例 3:
+<pre>
+<strong>输入:</strong> s = "aaa"
+<strong>输出:</strong> 3
+<strong>解释:</strong> 3 个不同的子序列分别是 "a", "aa" 以及 "aaa"。
+</pre>
+
+#### 提示:
+* `1 <= s.length <= 2000`
+* `s` 仅由小写英文字母组成
+
+## 题解 (Rust)
+
+### 1. 题解
+```Rust
+impl Solution {
+ pub fn distinct_subseq_ii(s: String) -> i32 {
+ const MOD: i32 = 1_000_000_007;
+ let n = s.len();
+ let mut last_index = [n; 26];
+ let mut dp = vec![0_i32; n + 1];
+ dp[n] = -1;
+
+ for (i, c) in s.bytes().map(|c| (c - b'a') as usize).enumerate() {
+ dp[i + 1] = (dp[i] * 2 - dp[last_index[c]]).rem_euclid(MOD);
+ last_index[c] = i;
+ }
+
+ *dp.last().unwrap()
+ }
+}
+```

Problemset/0940-Distinct Subsequences II/Solution.rs

@@ -0,0 +1,16 @@
+impl Solution {
+ pub fn distinct_subseq_ii(s: String) -> i32 {
+ const MOD: i32 = 1_000_000_007;
+ let n = s.len();
+ let mut last_index = [n; 26];
+ let mut dp = vec![0_i32; n + 1];
+ dp[n] = -1;
+
+ for (i, c) in s.bytes().map(|c| (c - b'a') as usize).enumerate() {
+ dp[i + 1] = (dp[i] * 2 - dp[last_index[c]]).rem_euclid(MOD);
+ last_index[c] = i;
+ }
+
+ *dp.last().unwrap()
+ }
+}

README.md

@@ -714,6 +714,7 @@
 [937][937l] |[Reorder Data in Log Files][937] |![py]
 [938][938l] |[Range Sum of BST][938] |![py]
 [939][939l] |[Minimum Area Rectangle][939] |![py]  ![rs]
+[940][940l] |[Distinct Subsequences II][940] |![rs]
 [941][941l] |[Valid Mountain Array][941] |![rs]
 [942][942l] |[DI String Match][942] |![py]
 [944][944l] |[Delete Columns to Make Sorted][944] |![py]
@@ -2645,6 +2646,7 @@
 [937]:Problemset/0937-Reorder%20Data%20in%20Log%20Files/README.md#937-reorder-data-in-log-files
 [938]:Problemset/0938-Range%20Sum%20of%20BST/README.md#938-range-sum-of-bst
 [939]:Problemset/0939-Minimum%20Area%20Rectangle/README.md#939-minimum-area-rectangle
+[940]:Problemset/0940-Distinct%20Subsequences%20II/README.md#940-distinct-subsequences-ii
 [941]:Problemset/0941-Valid%20Mountain%20Array/README.md#941-valid-mountain-array
 [942]:Problemset/0942-DI%20String%20Match/README.md#942-di-string-match
 [944]:Problemset/0944-Delete%20Columns%20to%20Make%20Sorted/README.md#944-delete-columns-to-make-sorted
@@ -4570,6 +4572,7 @@
 [937l]:https://leetcode.com/problems/reorder-data-in-log-files/
 [938l]:https://leetcode.com/problems/range-sum-of-bst/
 [939l]:https://leetcode.com/problems/minimum-area-rectangle/
+[940l]:https://leetcode.com/problems/distinct-subsequences-ii/
 [941l]:https://leetcode.com/problems/valid-mountain-array/
 [942l]:https://leetcode.com/problems/di-string-match/
 [944l]:https://leetcode.com/problems/delete-columns-to-make-sorted/

README_CN.md

@@ -714,6 +714,7 @@
 [937][937l] |[重新排列日志文件][937] |![py]
 [938][938l] |[二叉搜索树的范围和][938] |![py]
 [939][939l] |[最小面积矩形][939] |![py]  ![rs]
+[940][940l] |[不同的子序列 II][940] |![rs]
 [941][941l] |[有效的山脉数组][941] |![rs]
 [942][942l] |[增减字符串匹配][942] |![py]
 [944][944l] |[删列造序][944] |![py]
@@ -2645,6 +2646,7 @@
 [937]:Problemset/0937-Reorder%20Data%20in%20Log%20Files/README_CN.md#937-重新排列日志文件
 [938]:Problemset/0938-Range%20Sum%20of%20BST/README_CN.md#938-二叉搜索树的范围和
 [939]:Problemset/0939-Minimum%20Area%20Rectangle/README_CN.md#939-最小面积矩形
+[940]:Problemset/0940-Distinct%20Subsequences%20II/README_CN.md#940-不同的子序列-ii
 [941]:Problemset/0941-Valid%20Mountain%20Array/README_CN.md#941-有效的山脉数组
 [942]:Problemset/0942-DI%20String%20Match/README_CN.md#942-增减字符串匹配
 [944]:Problemset/0944-Delete%20Columns%20to%20Make%20Sorted/README_CN.md#944-删列造序
@@ -4570,6 +4572,7 @@
 [937l]:https://leetcode.cn/problems/reorder-data-in-log-files/
 [938l]:https://leetcode.cn/problems/range-sum-of-bst/
 [939l]:https://leetcode.cn/problems/minimum-area-rectangle/
+[940l]:https://leetcode.cn/problems/distinct-subsequences-ii/
 [941l]:https://leetcode.cn/problems/valid-mountain-array/
 [942l]:https://leetcode.cn/problems/di-string-match/
 [944l]:https://leetcode.cn/problems/delete-columns-to-make-sorted/