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feat: add solutions to lc problems: No.2255,2256 #1717

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yanglbme merged 1 commit into main from dev
Sep 28, 2023
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33 changes: 21 additions & 12 deletions solution/2200-2299/2255.Count Prefixes of a Given String/README.md
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,14 @@ words 中是 s = "abc" 前缀的字符串为:

<!-- 这里可写通用的实现逻辑 -->

**方法一:遍历计数**

我们直接遍历数组 $words,ドル对于每个字符串 $w,ドル判断 $s$ 是否以 $w$ 为前缀,如果是则答案加一。

遍历结束后,返回答案即可。

时间复杂度 $O(m \times n),ドル其中 $m$ 和 $n$ 分别是数组 $words$ 的长度和字符串 $s$ 的长度。空间复杂度 $O(1)$。

<!-- tabs:start -->

### **Python3**
Expand All @@ -54,7 +62,7 @@ words 中是 s = "abc" 前缀的字符串为:
```python
class Solution:
def countPrefixes(self, words: List[str], s: str) -> int:
return sum(word == s[: len(word)] for word in words)
return sum(s.startswith(w) for w in words)
```

### **Java**
Expand All @@ -65,8 +73,8 @@ class Solution:
class Solution {
public int countPrefixes(String[] words, String s) {
int ans = 0;
for (String word : words) {
if (word.equals(s.substring(0, Math.min(s.length(), word.length())))) {
for (String w : words) {
if (s.startsWith(w)) {
++ans;
}
}
Expand All @@ -82,9 +90,9 @@ class Solution {
public:
int countPrefixes(vector<string>& words, string s) {
int ans = 0;
for (auto& word : words)
if (s.substr(0, word.size()) == word)
++ans;
for (auto& w : words) {
ans += s.starts_with(w);
}
return ans;
}
};
Expand All @@ -93,21 +101,22 @@ public:
### **Go**

```go
func countPrefixes(words []string, s string) int {
ans := 0
for _, word := range words {
if strings.HasPrefix(s, word) {
func countPrefixes(words []string, s string) (ans int) {
for _, w := range words {
if strings.HasPrefix(s, w) {
ans++
}
}
return ans
return
}
```

### **TypeScript**

```ts

function countPrefixes(words: string[], s: string): number {
return words.filter(w => s.startsWith(w)).length;
}
```

### **...**
Expand Down
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Original file line number Diff line number Diff line change
Expand Up @@ -41,14 +41,22 @@ Note that the same string can occur multiple times in words, and it should be co

## Solutions

**Solution 1: Traversal Counting**

We directly traverse the array words, and for each string w, we check if s starts with w as a prefix. If it does, we increment the answer by one.

After the traversal, we return the answer.

The time complexity is $O(m \times n),ドル where $m$ and $n$ are the lengths of the array words and the string s, respectively. The space complexity is $O(1)$.

<!-- tabs:start -->

### **Python3**

```python
class Solution:
def countPrefixes(self, words: List[str], s: str) -> int:
return sum(word == s[: len(word)] for word in words)
return sum(s.startswith(w) for w in words)
```

### **Java**
Expand All @@ -57,8 +65,8 @@ class Solution:
class Solution {
public int countPrefixes(String[] words, String s) {
int ans = 0;
for (String word : words) {
if (word.equals(s.substring(0, Math.min(s.length(), word.length())))) {
for (String w : words) {
if (s.startsWith(w)) {
++ans;
}
}
Expand All @@ -74,9 +82,9 @@ class Solution {
public:
int countPrefixes(vector<string>& words, string s) {
int ans = 0;
for (auto& word : words)
if (s.substr(0, word.size()) == word)
++ans;
for (auto& w : words) {
ans += s.starts_with(w);
}
return ans;
}
};
Expand All @@ -85,21 +93,22 @@ public:
### **Go**

```go
func countPrefixes(words []string, s string) int {
ans := 0
for _, word := range words {
if strings.HasPrefix(s, word) {
func countPrefixes(words []string, s string) (ans int) {
for _, w := range words {
if strings.HasPrefix(s, w) {
ans++
}
}
return ans
return
}
```

### **TypeScript**

```ts

function countPrefixes(words: string[], s: string): number {
return words.filter(w => s.startsWith(w)).length;
}
```

### **...**
Expand Down
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Original file line number Diff line number Diff line change
@@ -1,10 +1,10 @@
class Solution {
public:
int countPrefixes(vector<string>& words, string s) {
int ans = 0;
for (auto& word : words)
if (s.substr(0, word.size()) == word)
++ans;
return ans;
}
class Solution {
public:
int countPrefixes(vector<string>& words, string s) {
int ans = 0;
for (auto& w : words) {
ans += s.starts_with(w);
}
return ans;
}
};
View file Open in desktop
Original file line number Diff line number Diff line change
@@ -1,9 +1,8 @@
func countPrefixes(words []string, s string) int {
ans := 0
for _, word := range words {
if strings.HasPrefix(s, word) {
func countPrefixes(words []string, s string) (ans int) {
for _, w := range words {
if strings.HasPrefix(s, w) {
ans++
}
}
return ans
return
}
View file Open in desktop
Original file line number Diff line number Diff line change
@@ -1,11 +1,11 @@
class Solution {
public int countPrefixes(String[] words, String s) {
int ans = 0;
for (String word : words) {
if (word.equals(s.substring(0, Math.min(s.length(), word.length())))) {
++ans;
}
}
return ans;
}
class Solution {
public int countPrefixes(String[] words, String s) {
int ans = 0;
for (String w : words) {
if (s.startsWith(w)) {
++ans;
}
}
return ans;
}
}
View file Open in desktop
Original file line number Diff line number Diff line change
@@ -1,3 +1,3 @@
class Solution:
def countPrefixes(self, words: List[str], s: str) -> int:
return sum(word == s[: len(word)] for word in words)
class Solution:
def countPrefixes(self, words: List[str], s: str) -> int:
return sum(s.startswith(w) for w in words)
View file Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
function countPrefixes(words: string[], s: string): number {
return words.filter(w => s.startsWith(w)).length;
}
105 changes: 66 additions & 39 deletions solution/2200-2299/2256.Minimum Average Difference/README.md
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,14 @@

<!-- 这里可写通用的实现逻辑 -->

**方法一:遍历**

我们直接遍历数组 $nums,ドル对于每个下标 $i,ドル维护前 $i + 1$ 个元素的和 $pre$ 和后 $n - i - 1$ 个元素的和 $suf,ドル计算平均差的绝对值 $t,ドル如果 $t$ 小于当前最小值 $mi,ドル则更新答案 $ans = i$ 和最小值 $mi = t$。

遍历结束后,返回答案即可。

时间复杂度 $O(n),ドル其中 $n$ 是数组 $nums$ 的长度。空间复杂度 $O(1)$。

<!-- tabs:start -->

### **Python3**
Expand All @@ -67,14 +75,15 @@
```python
class Solution:
def minimumAverageDifference(self, nums: List[int]) -> int:
s = list(accumulate(nums))
ans, n = 0, len(nums)
mi = inf
for i in range(n):
a = s[i] // (i + 1)
b = 0 if i == n - 1 else (s[-1] - s[i]) // (n - i - 1)
t = abs(a - b)
if mi > t:
pre, suf = 0, sum(nums)
n = len(nums)
ans, mi = 0, inf
for i, x in enumerate(nums):
pre += x
suf -= x
a = pre // (i + 1)
b = 0 if n - i - 1 == 0 else suf // (n - i - 1)
if (t := abs(a - b)) < mi:
ans = i
mi = t
return ans
Expand All @@ -88,18 +97,19 @@ class Solution:
class Solution {
public int minimumAverageDifference(int[] nums) {
int n = nums.length;
long[] s = new long[n];
s[0] = nums[0];
for (int i = 1; i < n; ++i) {
s[i] = s[i - 1] + nums[i];
long pre = 0, suf = 0;
for (int x : nums) {
suf += x;
}
int ans = 0;
long mi = Long.MAX_VALUE;
for (int i = 0; i < n; ++i) {
long a = s[i] / (i + 1);
long b = i == n - 1 ? 0 : (s[n - 1] - s[i]) / (n - i - 1);
pre += nums[i];
suf -= nums[i];
long a = pre / (i + 1);
long b = n - i - 1 == 0 ? 0 : suf / (n - i - 1);
long t = Math.abs(a - b);
if (mi > t) {
if (t < mi) {
ans = i;
mi = t;
}
Expand All @@ -112,22 +122,22 @@ class Solution {
### **C++**

```cpp
typedef long long ll;

class Solution {
public:
int minimumAverageDifference(vector<int>& nums) {
int n = nums.size();
vector<ll> s(n);
s[0] = nums[0];
for (int i = 1; i < n; ++i) s[i] = s[i - 1] + nums[i];
using ll = long long;
ll pre = 0;
ll suf = accumulate(nums.begin(), nums.end(), 0LL);
int ans = 0;
ll mi = LONG_MAX;
ll mi = suf;
for (int i = 0; i < n; ++i) {
ll a = s[i] / (i + 1);
ll b = i == n - 1 ? 0 : (s[n - 1] - s[i]) / (n - i - 1);
pre += nums[i];
suf -= nums[i];
ll a = pre / (i + 1);
ll b = n - i - 1 == 0 ? 0 : suf / (n - i - 1);
ll t = abs(a - b);
if (mi > t) {
if (t < mi) {
ans = i;
mi = t;
}
Expand All @@ -140,28 +150,27 @@ public:
### **Go**

```go
func minimumAverageDifference(nums []int) int {
func minimumAverageDifference(nums []int) (ans int) {
n := len(nums)
s := make([]int, n)
s[0] = nums[0]
for i := 1; i < n; i++ {
s[i] = s[i-1] + nums[i]
pre, suf := 0, 0
for _, x := range nums {
suf += x
}
ans := 0
mi := math.MaxInt32
for i := 0; i < n; i++ {
a := s[i] / (i + 1)
mi := suf
for i, x := range nums {
pre += x
suf -= x
a := pre / (i + 1)
b := 0
if i != n-1 {
b = (s[n-1] - s[i]) / (n - i - 1)
if n-i-1 != 0 {
b = suf / (n - i - 1)
}
t := abs(a - b)
if mi > t {
if t := abs(a - b); t < mi {
ans = i
mi = t
}
}
return ans
return
}

func abs(x int) int {
Expand All @@ -175,7 +184,25 @@ func abs(x int) int {
### **TypeScript**

```ts

function minimumAverageDifference(nums: number[]): number {
const n = nums.length;
let pre = 0;
let suf = nums.reduce((a, b) => a + b);
let ans = 0;
let mi = suf;
for (let i = 0; i < n; ++i) {
pre += nums[i];
suf -= nums[i];
const a = Math.floor(pre / (i + 1));
const b = n - i - 1 === 0 ? 0 : Math.floor(suf / (n - i - 1));
const t = Math.abs(a - b);
if (t < mi) {
ans = i;
mi = t;
}
}
return ans;
}
```

### **...**
Expand Down
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