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‎images/starcharts.svg

Lines changed: 18957 additions & 18428 deletions
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‎lcci/01.04.Palindrome Permutation/README.md

Lines changed: 83 additions & 31 deletions
Original file line numberDiff line numberDiff line change
@@ -25,7 +25,11 @@
2525

2626
<!-- 这里可写通用的实现逻辑 -->
2727

28-
用哈希表存储每个字符出现的次数。若次数为奇数的字符超过 1 个，则不是回文排列。
28+
**方法一：哈希表**
29+
30+
我们用哈希表 `cnt` 存储每个字符出现的次数。若次数为奇数的字符超过 $1$ 个，则不是回文排列。
31+
32+
时间复杂度 $O(n)$，空间复杂度 $O(n)$。其中 $n$ 为字符串长度。
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3034
<!-- tabs:start -->
3135

@@ -36,8 +40,20 @@
3640
```python
3741
class Solution:
3842
def canPermutePalindrome(self, s: str) -> bool:
39-
counter = Counter(s)
40-
return sum(1 for v in counter.values() if v % 2 == 1) <= 1
43+
cnt = Counter(s)
44+
return sum(v & 1 for v in cnt.values()) < 2
45+
```
46+
47+
```python
48+
class Solution:
49+
def canPermutePalindrome(self, s: str) -> bool:
50+
vis = set()
51+
for c in s:
52+
if c in vis:
53+
vis.remove(c)
54+
else:
55+
vis.add(c)
56+
return len(vis) < 2
4157
```
4258

4359
### **Java**
@@ -47,35 +63,31 @@ class Solution:
4763
```java
4864
class Solution {
4965
public boolean canPermutePalindrome(String s) {
50-
Map<Character, Integer> counter = new HashMap<>();
51-
for (char c : s.toCharArray()) {
52-
counter.put(c, counter.getOrDefault(c, 0) + 1);
66+
Map<Character, Integer> cnt = new HashMap<>();
67+
for (int i = 0; i < s.length(); ++i) {
68+
cnt.merge(s.charAt(i), 1, Integer::sum);
5369
}
54-
int cnt = 0;
55-
for (int v : counter.values()) {
56-
cnt += v % 2;
70+
int sum = 0;
71+
for (int v : cnt.values()) {
72+
sum += v & 1;
5773
}
58-
return cnt < 2;
74+
return sum < 2;
5975
}
6076
}
6177
```
6278

63-
### **Go**
64-
65-
```go
66-
func canPermutePalindrome(s string) bool {
67-
m := make(map[rune]bool)
68-
count := 0
69-
for _, r := range s {
70-
if m[r] {
71-
m[r] = false
72-
count--
73-
} else {
74-
m[r] = true
75-
count++
76-
}
77-
}
78-
return count <= 1
79+
```java
80+
class Solution {
81+
public boolean canPermutePalindrome(String s) {
82+
Set<Character> vis = new HashSet<>();
83+
for (int i = 0; i < s.length(); ++i) {
84+
char c = s.charAt(i);
85+
if (!vis.add(c)) {
86+
vis.remove(c);
87+
}
88+
}
89+
return vis.size() < 2;
90+
}
7991
}
8092
```
8193

@@ -85,15 +97,55 @@ func canPermutePalindrome(s string) bool {
8597
class Solution {
8698
public:
8799
bool canPermutePalindrome(string s) {
88-
unordered_map<char, int> counter;
89-
for (char c : s) ++counter[c];
90-
int cnt = 0;
91-
for (auto& [k, v] : counter) cnt += v % 2;
92-
return cnt < 2;
100+
unordered_map<char, int> cnt;
101+
for (auto& c : s) {
102+
++cnt[c];
103+
}
104+
int sum = 0;
105+
for (auto& [_, v] : cnt) {
106+
sum += v & 1;
107+
}
108+
return sum < 2;
93109
}
94110
};
95111
```
96112
113+
```cpp
114+
class Solution {
115+
public:
116+
bool canPermutePalindrome(string s) {
117+
unordered_set<char> vis;
118+
for (auto& c : s) {
119+
if (vis.count(c)) {
120+
vis.erase(c);
121+
} else {
122+
vis.insert(c);
123+
}
124+
}
125+
return vis.size() < 2;
126+
}
127+
};
128+
```
129+
130+
### **Go**
131+
132+
```go
133+
func canPermutePalindrome(s string) bool {
134+
vis := map[rune]bool{}
135+
cnt := 0
136+
for _, c := range s {
137+
if vis[c] {
138+
vis[c] = false
139+
cnt--
140+
} else {
141+
vis[c] = true
142+
cnt++
143+
}
144+
}
145+
return cnt < 2
146+
}
147+
```
148+
97149
### **TypeScript**
98150

99151
```ts

‎lcci/01.04.Palindrome Permutation/README_EN.md

Lines changed: 78 additions & 30 deletions
Original file line numberDiff line numberDiff line change
@@ -27,44 +27,52 @@
2727
```python
2828
class Solution:
2929
def canPermutePalindrome(self, s: str) -> bool:
30-
counter = Counter(s)
31-
return sum(1 for v in counter.values() if v % 2 == 1) <= 1
30+
cnt = Counter(s)
31+
return sum(v & 1 for v in cnt.values()) < 2
32+
```
33+
34+
```python
35+
class Solution:
36+
def canPermutePalindrome(self, s: str) -> bool:
37+
vis = set()
38+
for c in s:
39+
if c in vis:
40+
vis.remove(c)
41+
else:
42+
vis.add(c)
43+
return len(vis) < 2
3244
```
3345

3446
### **Java**
3547

3648
```java
3749
class Solution {
3850
public boolean canPermutePalindrome(String s) {
39-
Map<Character, Integer> counter = new HashMap<>();
40-
for (char c : s.toCharArray()) {
41-
counter.put(c, counter.getOrDefault(c, 0) + 1);
51+
Map<Character, Integer> cnt = new HashMap<>();
52+
for (int i = 0; i < s.length(); ++i) {
53+
cnt.merge(s.charAt(i), 1, Integer::sum);
4254
}
43-
int cnt = 0;
44-
for (int v : counter.values()) {
45-
cnt += v % 2;
55+
int sum = 0;
56+
for (int v : cnt.values()) {
57+
sum += v & 1;
4658
}
47-
return cnt < 2;
59+
return sum < 2;
4860
}
4961
}
5062
```
5163

52-
### **Go**
53-
54-
```go
55-
func canPermutePalindrome(s string) bool {
56-
m := make(map[rune]bool)
57-
count := 0
58-
for _, r := range s {
59-
if m[r] {
60-
m[r] = false
61-
count--
62-
} else {
63-
m[r] = true
64-
count++
65-
}
66-
}
67-
return count <= 1
64+
```java
65+
class Solution {
66+
public boolean canPermutePalindrome(String s) {
67+
Set<Character> vis = new HashSet<>();
68+
for (int i = 0; i < s.length(); ++i) {
69+
char c = s.charAt(i);
70+
if (!vis.add(c)) {
71+
vis.remove(c);
72+
}
73+
}
74+
return vis.size() < 2;
75+
}
6876
}
6977
```
7078

@@ -74,15 +82,55 @@ func canPermutePalindrome(s string) bool {
7482
class Solution {
7583
public:
7684
bool canPermutePalindrome(string s) {
77-
unordered_map<char, int> counter;
78-
for (char c : s) ++counter[c];
79-
int cnt = 0;
80-
for (auto& [k, v] : counter) cnt += v % 2;
81-
return cnt < 2;
85+
unordered_map<char, int> cnt;
86+
for (auto& c : s) {
87+
++cnt[c];
88+
}
89+
int sum = 0;
90+
for (auto& [_, v] : cnt) {
91+
sum += v & 1;
92+
}
93+
return sum < 2;
8294
}
8395
};
8496
```
8597
98+
```cpp
99+
class Solution {
100+
public:
101+
bool canPermutePalindrome(string s) {
102+
unordered_set<char> vis;
103+
for (auto& c : s) {
104+
if (vis.count(c)) {
105+
vis.erase(c);
106+
} else {
107+
vis.insert(c);
108+
}
109+
}
110+
return vis.size() < 2;
111+
}
112+
};
113+
```
114+
115+
### **Go**
116+
117+
```go
118+
func canPermutePalindrome(s string) bool {
119+
vis := map[rune]bool{}
120+
cnt := 0
121+
for _, c := range s {
122+
if vis[c] {
123+
vis[c] = false
124+
cnt--
125+
} else {
126+
vis[c] = true
127+
cnt++
128+
}
129+
}
130+
return cnt < 2
131+
}
132+
```
133+
86134
### **TypeScript**
87135

88136
```ts

‎lcci/01.04.Palindrome Permutation/Solution.cpp

Lines changed: 9 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1,10 +1,14 @@
11
class Solution {
22
public:
33
bool canPermutePalindrome(string s) {
4-
unordered_map<char, int> counter;
5-
for (char c : s) ++counter[c];
6-
int cnt = 0;
7-
for (auto& [k, v] : counter) cnt += v % 2;
8-
return cnt < 2;
4+
unordered_map<char, int> cnt;
5+
for (auto& c : s) {
6+
++cnt[c];
7+
}
8+
int sum = 0;
9+
for (auto& [_, v] : cnt) {
10+
sum += v & 1;
11+
}
12+
return sum < 2;
913
}
1014
};

‎lcci/01.04.Palindrome Permutation/Solution.go

Lines changed: 10 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -1,14 +1,14 @@
11
func canPermutePalindrome(s string) bool {
2-
m := make(map[rune]bool)
3-
count := 0
4-
for _, r := range s {
5-
if m[r] {
6-
m[r] = false
7-
count--
2+
vis := map[rune]bool{}
3+
cnt := 0
4+
for _, c := range s {
5+
if vis[c] {
6+
vis[c] = false
7+
cnt--
88
} else {
9-
m[r] = true
10-
count++
9+
vis[c] = true
10+
cnt++
1111
}
1212
}
13-
return count <= 1
14-
}
13+
return cnt < 2
14+
}

‎lcci/01.04.Palindrome Permutation/Solution.java

Lines changed: 7 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -1,13 +1,13 @@
11
class Solution {
22
public boolean canPermutePalindrome(String s) {
3-
Map<Character, Integer> counter = new HashMap<>();
4-
for (char c : s.toCharArray()) {
5-
counter.put(c, counter.getOrDefault(c, 0) + 1);
3+
Map<Character, Integer> cnt = new HashMap<>();
4+
for (int i = 0; i < s.length(); ++i) {
5+
cnt.merge(s.charAt(i), 1, Integer::sum);
66
}
7-
int cnt = 0;
8-
for (int v : counter.values()) {
9-
cnt += v % 2;
7+
int sum = 0;
8+
for (int v : cnt.values()) {
9+
sum += v & 1;
1010
}
11-
return cnt < 2;
11+
return sum < 2;
1212
}
1313
}

‎lcci/01.04.Palindrome Permutation/Solution.py

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
11
class Solution:
22
def canPermutePalindrome(self, s: str) -> bool:
3-
counter = Counter(s)
4-
return sum(1 for v in counter.values() if v % 2 == 1) <= 1
3+
cnt = Counter(s)
4+
return sum(v & 1 for v in cnt.values()) < 2

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