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feat: add solutions to lc problem: No.2207 (doocs#3536)
No.2207.Maximize Number of Subsequences in a String
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‎solution/2200-2299/2207.Maximize Number of Subsequences in a String/README.md

Lines changed: 67 additions & 30 deletions
Original file line numberDiff line numberDiff line change
@@ -67,7 +67,18 @@ tags:
6767

6868
<!-- solution:start -->
6969

70-
### 方法一
70+
### 方法一：遍历 + 计数
71+
72+
我们可以使用两个变量 $x$ 和 $y$ 分别记录当前字符串中 $\textit{pattern}[0]$ 和 $\textit{pattern}[1]$ 出现的次数。
73+
74+
然后遍历字符串 $\textit{text}$，对于当前遍历到的字符 $c$：
75+
76+
- 如果 $c$ 等于 $\textit{pattern}[1]$，我们将 $y$ 加一，此时之前出现过的所有 $\textit{pattern}[0]$ 都可以和当前的 $c$ 组成一个 $\textit{pattern}$ 子序列，因此答案加上 $x$；
77+
- 如果 $c$ 等于 $\textit{pattern}[0]$，我们将 $x$ 加一。
78+
79+
遍历结束后，由于我们可以插入一个字符，因此，如果我们在字符串开头加上 $\textit{pattern}[0]$，那么可以得到 $y$ 个 $\textit{pattern}$ 子序列；如果我们在字符串结尾加上 $\textit{pattern}[1]$，那么可以得到 $x$ 个 $\textit{pattern}$ 子序列。因此，我们将答案加上 $x$ 和 $y$ 中的较大值即可。
80+
81+
时间复杂度 $O(n)$，其中 $n$ 为字符串 $\textit{text}$ 的长度。空间复杂度 $O(1)$。
7182

7283
<!-- tabs:start -->
7384

@@ -76,13 +87,14 @@ tags:
7687
```python
7788
class Solution:
7889
def maximumSubsequenceCount(self, text: str, pattern: str) -> int:
79-
ans = 0
80-
cnt = Counter()
90+
ans = x = y = 0
8191
for c in text:
8292
if c == pattern[1]:
83-
ans += cnt[pattern[0]]
84-
cnt[c] += 1
85-
ans += max(cnt[pattern[0]], cnt[pattern[1]])
93+
y += 1
94+
ans += x
95+
if c == pattern[0]:
96+
x += 1
97+
ans += max(x, y)
8698
return ans
8799
```
88100

@@ -91,17 +103,18 @@ class Solution:
91103
```java
92104
class Solution {
93105
public long maximumSubsequenceCount(String text, String pattern) {
94-
int[] cnt = new int[26];
95-
char a = pattern.charAt(0);
96-
char b = pattern.charAt(1);
97106
long ans = 0;
98-
for (char c : text.toCharArray()) {
99-
if (c == b) {
100-
ans += cnt[a - 'a'];
107+
int x = 0, y = 0;
108+
for (int i = 0; i < text.length(); ++i) {
109+
if (text.charAt(i) == pattern.charAt(1)) {
110+
++y;
111+
ans += x;
112+
}
113+
if (text.charAt(i) == pattern.charAt(0)) {
114+
++x;
101115
}
102-
cnt[c - 'a']++;
103116
}
104-
ans += Math.max(cnt[a - 'a'], cnt[b - 'a']);
117+
ans += Math.max(x, y);
105118
return ans;
106119
}
107120
}
@@ -114,13 +127,17 @@ class Solution {
114127
public:
115128
long long maximumSubsequenceCount(string text, string pattern) {
116129
long long ans = 0;
117-
char a = pattern[0], b = pattern[1];
118-
vector<int> cnt(26);
130+
int x = 0, y = 0;
119131
for (char& c : text) {
120-
if (c == b) ans += cnt[a - 'a'];
121-
cnt[c - 'a']++;
132+
if (c == pattern[1]) {
133+
++y;
134+
ans += x;
135+
}
136+
if (c == pattern[0]) {
137+
++x;
138+
}
122139
}
123-
ans += max(cnt[a - 'a'], cnt[b - 'a']);
140+
ans += max(x, y);
124141
return ans;
125142
}
126143
};
@@ -129,19 +146,39 @@ public:
129146
#### Go
130147
131148
```go
132-
func maximumSubsequenceCount(text string, pattern string) int64 {
133-
ans := 0
134-
cnt := make([]int, 26)
135-
a, b := pattern[0], pattern[1]
136-
for i := range text {
137-
c := text[i]
138-
if c == b {
139-
ans += cnt[a-'a']
149+
func maximumSubsequenceCount(text string, pattern string) (ans int64) {
150+
x, y := 0, 0
151+
for _, c := range text {
152+
if byte(c) == pattern[1] {
153+
y++
154+
ans += int64(x)
155+
}
156+
if byte(c) == pattern[0] {
157+
x++
140158
}
141-
cnt[c-'a']++
142159
}
143-
ans += max(cnt[a-'a'], cnt[b-'a'])
144-
return int64(ans)
160+
ans += int64(max(x, y))
161+
return
162+
}
163+
```
164+
165+
#### TypeScript
166+
167+
```ts
168+
function maximumSubsequenceCount(text: string, pattern: string): number {
169+
let ans = 0;
170+
let [x, y] = [0, 0];
171+
for (const c of text) {
172+
if (c === pattern[1]) {
173+
++y;
174+
ans += x;
175+
}
176+
if (c === pattern[0]) {
177+
++x;
178+
}
179+
}
180+
ans += Math.max(x, y);
181+
return ans;
145182
}
146183
```
147184

‎solution/2200-2299/2207.Maximize Number of Subsequences in a String/README_EN.md

Lines changed: 67 additions & 30 deletions
Original file line numberDiff line numberDiff line change
@@ -65,7 +65,18 @@ Some of the strings which can be obtained from text and have 6 subsequences &quo
6565

6666
<!-- solution:start -->
6767

68-
### Solution 1
68+
### Solution 1: Traversal + Counting
69+
70+
We can use two variables $x$ and $y$ to record the current counts of $\textit{pattern}[0]$ and $\textit{pattern}[1]$ in the string, respectively.
71+
72+
Then, traverse the string $\textit{text}$. For the current character $c$:
73+
74+
- If $c$ equals $\textit{pattern}[1]$, increment $y$ by one. At this point, all previously encountered $\textit{pattern}[0]$ can form a $\textit{pattern}$ subsequence with the current $c$, so add $x$ to the answer.
75+
- If $c$ equals $\textit{pattern}[0]$, increment $x$ by one.
76+
77+
After the traversal, since we can insert one character, if we add $\textit{pattern}[0]$ at the beginning of the string, we can get $y$ $\textit{pattern}$ subsequences. If we add $\textit{pattern}[1]$ at the end of the string, we can get $x$ $\textit{pattern}$ subsequences. Therefore, we add the larger value of $x$ and $y$ to the answer.
78+
79+
The time complexity is $O(n)$, where $n$ is the length of the string $\textit{text}$. The space complexity is $O(1)$.
6980

7081
<!-- tabs:start -->
7182

@@ -74,13 +85,14 @@ Some of the strings which can be obtained from text and have 6 subsequences &quo
7485
```python
7586
class Solution:
7687
def maximumSubsequenceCount(self, text: str, pattern: str) -> int:
77-
ans = 0
78-
cnt = Counter()
88+
ans = x = y = 0
7989
for c in text:
8090
if c == pattern[1]:
81-
ans += cnt[pattern[0]]
82-
cnt[c] += 1
83-
ans += max(cnt[pattern[0]], cnt[pattern[1]])
91+
y += 1
92+
ans += x
93+
if c == pattern[0]:
94+
x += 1
95+
ans += max(x, y)
8496
return ans
8597
```
8698

@@ -89,17 +101,18 @@ class Solution:
89101
```java
90102
class Solution {
91103
public long maximumSubsequenceCount(String text, String pattern) {
92-
int[] cnt = new int[26];
93-
char a = pattern.charAt(0);
94-
char b = pattern.charAt(1);
95104
long ans = 0;
96-
for (char c : text.toCharArray()) {
97-
if (c == b) {
98-
ans += cnt[a - 'a'];
105+
int x = 0, y = 0;
106+
for (int i = 0; i < text.length(); ++i) {
107+
if (text.charAt(i) == pattern.charAt(1)) {
108+
++y;
109+
ans += x;
110+
}
111+
if (text.charAt(i) == pattern.charAt(0)) {
112+
++x;
99113
}
100-
cnt[c - 'a']++;
101114
}
102-
ans += Math.max(cnt[a - 'a'], cnt[b - 'a']);
115+
ans += Math.max(x, y);
103116
return ans;
104117
}
105118
}
@@ -112,13 +125,17 @@ class Solution {
112125
public:
113126
long long maximumSubsequenceCount(string text, string pattern) {
114127
long long ans = 0;
115-
char a = pattern[0], b = pattern[1];
116-
vector<int> cnt(26);
128+
int x = 0, y = 0;
117129
for (char& c : text) {
118-
if (c == b) ans += cnt[a - 'a'];
119-
cnt[c - 'a']++;
130+
if (c == pattern[1]) {
131+
++y;
132+
ans += x;
133+
}
134+
if (c == pattern[0]) {
135+
++x;
136+
}
120137
}
121-
ans += max(cnt[a - 'a'], cnt[b - 'a']);
138+
ans += max(x, y);
122139
return ans;
123140
}
124141
};
@@ -127,19 +144,39 @@ public:
127144
#### Go
128145
129146
```go
130-
func maximumSubsequenceCount(text string, pattern string) int64 {
131-
ans := 0
132-
cnt := make([]int, 26)
133-
a, b := pattern[0], pattern[1]
134-
for i := range text {
135-
c := text[i]
136-
if c == b {
137-
ans += cnt[a-'a']
147+
func maximumSubsequenceCount(text string, pattern string) (ans int64) {
148+
x, y := 0, 0
149+
for _, c := range text {
150+
if byte(c) == pattern[1] {
151+
y++
152+
ans += int64(x)
153+
}
154+
if byte(c) == pattern[0] {
155+
x++
138156
}
139-
cnt[c-'a']++
140157
}
141-
ans += max(cnt[a-'a'], cnt[b-'a'])
142-
return int64(ans)
158+
ans += int64(max(x, y))
159+
return
160+
}
161+
```
162+
163+
#### TypeScript
164+
165+
```ts
166+
function maximumSubsequenceCount(text: string, pattern: string): number {
167+
let ans = 0;
168+
let [x, y] = [0, 0];
169+
for (const c of text) {
170+
if (c === pattern[1]) {
171+
++y;
172+
ans += x;
173+
}
174+
if (c === pattern[0]) {
175+
++x;
176+
}
177+
}
178+
ans += Math.max(x, y);
179+
return ans;
143180
}
144181
```
145182

‎solution/2200-2299/2207.Maximize Number of Subsequences in a String/Solution.cpp

Lines changed: 10 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -2,13 +2,17 @@ class Solution {
22
public:
33
long long maximumSubsequenceCount(string text, string pattern) {
44
long long ans = 0;
5-
char a = pattern[0], b = pattern[1];
6-
vector<int> cnt(26);
5+
int x = 0, y = 0;
76
for (char& c : text) {
8-
if (c == b) ans += cnt[a - 'a'];
9-
cnt[c - 'a']++;
7+
if (c == pattern[1]) {
8+
++y;
9+
ans += x;
10+
}
11+
if (c == pattern[0]) {
12+
++x;
13+
}
1014
}
11-
ans += max(cnt[a - 'a'], cnt[b - 'a']);
15+
ans += max(x, y);
1216
return ans;
1317
}
14-
};
18+
};

‎solution/2200-2299/2207.Maximize Number of Subsequences in a String/Solution.go

Lines changed: 12 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -1,14 +1,14 @@
1-
func maximumSubsequenceCount(text string, pattern string) int64 {
2-
ans := 0
3-
cnt := make([]int, 26)
4-
a, b := pattern[0], pattern[1]
5-
for i := range text {
6-
c := text[i]
7-
if c == b {
8-
ans += cnt[a-'a']
1+
func maximumSubsequenceCount(text string, pattern string) (ans int64) {
2+
x, y := 0, 0
3+
for _, c := range text {
4+
if byte(c) == pattern[1] {
5+
y++
6+
ans += int64(x)
7+
}
8+
if byte(c) == pattern[0] {
9+
x++
910
}
10-
cnt[c-'a']++
1111
}
12-
ans += max(cnt[a-'a'], cnt[b-'a'])
13-
return int64(ans)
14-
}
12+
ans += int64(max(x, y))
13+
return
14+
}

‎solution/2200-2299/2207.Maximize Number of Subsequences in a String/Solution.java

Lines changed: 10 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -1,16 +1,17 @@
11
class Solution {
22
public long maximumSubsequenceCount(String text, String pattern) {
3-
int[] cnt = new int[26];
4-
char a = pattern.charAt(0);
5-
char b = pattern.charAt(1);
63
long ans = 0;
7-
for (char c : text.toCharArray()) {
8-
if (c == b) {
9-
ans += cnt[a - 'a'];
4+
int x = 0, y = 0;
5+
for (int i = 0; i < text.length(); ++i) {
6+
if (text.charAt(i) == pattern.charAt(1)) {
7+
++y;
8+
ans += x;
9+
}
10+
if (text.charAt(i) == pattern.charAt(0)) {
11+
++x;
1012
}
11-
cnt[c - 'a']++;
1213
}
13-
ans += Math.max(cnt[a - 'a'], cnt[b - 'a']);
14+
ans += Math.max(x, y);
1415
return ans;
1516
}
16-
}
17+
}

‎solution/2200-2299/2207.Maximize Number of Subsequences in a String/Solution.py

Lines changed: 6 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1,10 +1,11 @@
11
class Solution:
22
def maximumSubsequenceCount(self, text: str, pattern: str) -> int:
3-
ans = 0
4-
cnt = Counter()
3+
ans = x = y = 0
54
for c in text:
65
if c == pattern[1]:
7-
ans += cnt[pattern[0]]
8-
cnt[c] += 1
9-
ans += max(cnt[pattern[0]], cnt[pattern[1]])
6+
y += 1
7+
ans += x
8+
if c == pattern[0]:
9+
x += 1
10+
ans += max(x, y)
1011
return ans

‎solution/2200-2299/2207.Maximize Number of Subsequences in a String/Solution.ts

Lines changed: 15 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,15 @@
1+
function maximumSubsequenceCount(text: string, pattern: string): number {
2+
let ans = 0;
3+
let [x, y] = [0, 0];
4+
for (const c of text) {
5+
if (c === pattern[1]) {
6+
++y;
7+
ans += x;
8+
}
9+
if (c === pattern[0]) {
10+
++x;
11+
}
12+
}
13+
ans += Math.max(x, y);
14+
return ans;
15+
}

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