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feat: add solutions to lc problems: No.2859~2861 (doocs#1644)
* No.2859.Sum of Values at Indices With K Set Bits * No.2860.Happy Students * No.2861.Maximum Number of Alloys
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‎solution/2800-2899/2859.Sum of Values at Indices With K Set Bits/README.md

+53-2
Original file line numberDiff line numberDiff line change
@@ -58,14 +58,24 @@
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<!-- 这里可写通用的实现逻辑 -->
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**方法一：模拟**
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我们直接遍历每个下标 $i$，判断其二进制表示中 $1$ 的个数是否等于 $k$，如果等于则将其对应的元素累加到答案 $ans$ 中。
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遍历结束后，返回答案即可。
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时间复杂度 $O(n \times \log n)$，其中 $n$ 是数组 $nums$ 的长度。空间复杂度 $O(1)$。
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<!-- tabs:start -->
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### **Python3**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```python
68-
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class Solution:
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def sumIndicesWithKSetBits(self, nums: List[int], k: int) -> int:
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return sum(x for i, x in enumerate(nums) if i.bit_count() == k)
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```
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7181
### **Java**
@@ -89,13 +99,54 @@ class Solution {
8999
### **C++**
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```cpp
92-
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class Solution {
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public:
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int sumIndicesWithKSetBits(vector<int>& nums, int k) {
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int ans = 0;
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for (int i = 0; i < nums.size(); ++i) {
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if (__builtin_popcount(i) == k) {
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ans += nums[i];
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}
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}
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return ans;
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}
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};
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```
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### **Go**
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```go
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func sumIndicesWithKSetBits(nums []int, k int) (ans int) {
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for i, x := range nums {
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if bits.OnesCount(uint(i)) == k {
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ans += x
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}
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}
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return
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}
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```
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### **TypeScript**
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```ts
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function sumIndicesWithKSetBits(nums: number[], k: number): number {
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let ans = 0;
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for (let i = 0; i < nums.length; ++i) {
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if (bitCount(i) === k) {
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ans += nums[i];
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}
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}
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return ans;
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}
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function bitCount(n: number): number {
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let count = 0;
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while (n) {
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n &= n - 1;
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count++;
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}
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return count;
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}
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```
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### **...**

‎solution/2800-2899/2859.Sum of Values at Indices With K Set Bits/README_EN.md

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Original file line numberDiff line numberDiff line change
@@ -59,7 +59,9 @@ Hence, the answer is nums[3] = 1.
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### **Python3**
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```python
62-
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class Solution:
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def sumIndicesWithKSetBits(self, nums: List[int], k: int) -> int:
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return sum(x for i, x in enumerate(nums) if i.bit_count() == k)
6365
```
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### **Java**
@@ -81,13 +83,54 @@ class Solution {
8183
### **C++**
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```cpp
84-
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class Solution {
87+
public:
88+
int sumIndicesWithKSetBits(vector<int>& nums, int k) {
89+
int ans = 0;
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for (int i = 0; i < nums.size(); ++i) {
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if (__builtin_popcount(i) == k) {
92+
ans += nums[i];
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}
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}
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return ans;
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}
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};
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```
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### **Go**
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```go
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func sumIndicesWithKSetBits(nums []int, k int) (ans int) {
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for i, x := range nums {
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if bits.OnesCount(uint(i)) == k {
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ans += x
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}
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}
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return
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}
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```
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### **TypeScript**
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```ts
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function sumIndicesWithKSetBits(nums: number[], k: number): number {
117+
let ans = 0;
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for (let i = 0; i < nums.length; ++i) {
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if (bitCount(i) === k) {
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ans += nums[i];
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}
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}
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return ans;
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}
90125

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function bitCount(n: number): number {
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let count = 0;
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while (n) {
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n &= n - 1;
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count++;
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}
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return count;
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}
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```
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### **...**

‎solution/2800-2899/2859.Sum of Values at Indices With K Set Bits/Solution.cpp

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class Solution {
2+
public:
3+
int sumIndicesWithKSetBits(vector<int>& nums, int k) {
4+
int ans = 0;
5+
for (int i = 0; i < nums.size(); ++i) {
6+
if (__builtin_popcount(i) == k) {
7+
ans += nums[i];
8+
}
9+
}
10+
return ans;
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}
12+
};

‎solution/2800-2899/2859.Sum of Values at Indices With K Set Bits/Solution.go

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,8 @@
1+
func sumIndicesWithKSetBits(nums []int, k int) (ans int) {
2+
for i, x := range nums {
3+
if bits.OnesCount(uint(i)) == k {
4+
ans += x
5+
}
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}
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return
8+
}

‎solution/2800-2899/2859.Sum of Values at Indices With K Set Bits/Solution.py

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@@ -0,0 +1,3 @@
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class Solution:
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def sumIndicesWithKSetBits(self, nums: List[int], k: int) -> int:
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return sum(x for i, x in enumerate(nums) if i.bit_count() == k)

‎solution/2800-2899/2859.Sum of Values at Indices With K Set Bits/Solution.ts

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Original file line numberDiff line numberDiff line change
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1+
function sumIndicesWithKSetBits(nums: number[], k: number): number {
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let ans = 0;
3+
for (let i = 0; i < nums.length; ++i) {
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if (bitCount(i) === k) {
5+
ans += nums[i];
6+
}
7+
}
8+
return ans;
9+
}
10+
11+
function bitCount(n: number): number {
12+
let count = 0;
13+
while (n) {
14+
n &= n - 1;
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count++;
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}
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return count;
18+
}

‎solution/2800-2899/2860.Happy Students/README.md

+69-2
Original file line numberDiff line numberDiff line change
@@ -56,14 +56,40 @@
5656

5757
<!-- 这里可写通用的实现逻辑 -->
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**方法一：排序 + 枚举**
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假设选出了 $k$ 个学生，那么以下情况成立：
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- 如果 $nums[i] = k$，那么不存在分组方法；
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- 如果 $nums[i] \gt k$，那么学生 $i$ 不被选中；
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- 如果 $nums[i] \lt k$，那么学生 $i$ 被选中。
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因此，被选中的学生一定是排序后的 $nums$ 数组中的前 $k$ 个元素。
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我们在 $[0,..n]$ 范围内枚举 $k$，对于当前选出的学生人数 $i$，我们可以得到组内最大的学生编号 $i-1$，数字为 $nums[i-1]$。如果 $i \gt 0$ 并且 $nums[i-1] \ge i$，那么不存在分组方法；如果 $i \lt n$ 并且 $nums[i] \le i$，那么不存在分组方法。否则，存在分组方法，答案加一。
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枚举结束后，返回答案即可。
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时间复杂度 $O(n \times \log n)$，空间复杂度 $O(\log n)$。其中 $n$ 为数组长度。
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5975
<!-- tabs:start -->
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### **Python3**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```python
66-
82+
class Solution:
83+
def countWays(self, nums: List[int]) -> int:
84+
nums.sort()
85+
n = len(nums)
86+
ans = 0
87+
for i in range(n + 1):
88+
if i and nums[i - 1] >= i:
89+
continue
90+
if i < n and nums[i] <= i:
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continue
92+
return ans
6793
```
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### **Java**
@@ -89,13 +115,54 @@ class Solution {
89115
### **C++**
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91117
```cpp
92-
118+
class Solution {
119+
public:
120+
int countWays(vector<int>& nums) {
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sort(nums.begin(), nums.end());
122+
int ans = 0;
123+
int n = nums.size();
124+
for (int i = 0; i <= n; ++i) {
125+
if ((i && nums[i - 1] >= i) || (i < n && nums[i] <= i)) {
126+
continue;
127+
}
128+
++ans;
129+
}
130+
return ans;
131+
}
132+
};
93133
```
94134
95135
### **Go**
96136
97137
```go
138+
func countWays(nums []int) (ans int) {
139+
sort.Ints(nums)
140+
n := len(nums)
141+
for i := 0; i <= n; i++ {
142+
if (i > 0 && nums[i-1] >= i) || (i < n && nums[i] <= i) {
143+
continue
144+
}
145+
ans++
146+
}
147+
return
148+
}
149+
```
150+
151+
### **TypeScript**
98152

153+
```ts
154+
function countWays(nums: number[]): number {
155+
nums.sort((a, b) => a - b);
156+
let ans = 0;
157+
const n = nums.length;
158+
for (let i = 0; i <= n; ++i) {
159+
if ((i && nums[i - 1] >= i) || (i < n && nums[i] <= i)) {
160+
continue;
161+
}
162+
++ans;
163+
}
164+
return ans;
165+
}
99166
```
100167

101168
### **...**

‎solution/2800-2899/2860.Happy Students/README_EN.md

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Original file line numberDiff line numberDiff line change
@@ -55,7 +55,17 @@ The class teacher selects all the students to form the group.
5555
### **Python3**
5656

5757
```python
58-
58+
class Solution:
59+
def countWays(self, nums: List[int]) -> int:
60+
nums.sort()
61+
n = len(nums)
62+
ans = 0
63+
for i in range(n + 1):
64+
if i and nums[i - 1] >= i:
65+
continue
66+
if i < n and nums[i] <= i:
67+
continue
68+
return ans
5969
```
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6171
### **Java**
@@ -79,13 +89,54 @@ class Solution {
7989
### **C++**
8090

8191
```cpp
82-
92+
class Solution {
93+
public:
94+
int countWays(vector<int>& nums) {
95+
sort(nums.begin(), nums.end());
96+
int ans = 0;
97+
int n = nums.size();
98+
for (int i = 0; i <= n; ++i) {
99+
if ((i && nums[i - 1] >= i) || (i < n && nums[i] <= i)) {
100+
continue;
101+
}
102+
++ans;
103+
}
104+
return ans;
105+
}
106+
};
83107
```
84108
85109
### **Go**
86110
87111
```go
112+
func countWays(nums []int) (ans int) {
113+
sort.Ints(nums)
114+
n := len(nums)
115+
for i := 0; i <= n; i++ {
116+
if (i > 0 && nums[i-1] >= i) || (i < n && nums[i] <= i) {
117+
continue
118+
}
119+
ans++
120+
}
121+
return
122+
}
123+
```
124+
125+
### **TypeScript**
88126

127+
```ts
128+
function countWays(nums: number[]): number {
129+
nums.sort((a, b) => a - b);
130+
let ans = 0;
131+
const n = nums.length;
132+
for (let i = 0; i <= n; ++i) {
133+
if ((i && nums[i - 1] >= i) || (i < n && nums[i] <= i)) {
134+
continue;
135+
}
136+
++ans;
137+
}
138+
return ans;
139+
}
89140
```
90141

91142
### **...**

‎solution/2800-2899/2860.Happy Students/Solution.cpp

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Original file line numberDiff line numberDiff line change
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1+
class Solution {
2+
public:
3+
int countWays(vector<int>& nums) {
4+
sort(nums.begin(), nums.end());
5+
int ans = 0;
6+
int n = nums.size();
7+
for (int i = 0; i <= n; ++i) {
8+
if ((i && nums[i - 1] >= i) || (i < n && nums[i] <= i)) {
9+
continue;
10+
}
11+
++ans;
12+
}
13+
return ans;
14+
}
15+
};

‎solution/2800-2899/2860.Happy Students/Solution.go

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Original file line numberDiff line numberDiff line change
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1+
func countWays(nums []int) (ans int) {
2+
sort.Ints(nums)
3+
n := len(nums)
4+
for i := 0; i <= n; i++ {
5+
if (i > 0 && nums[i-1] >= i) || (i < n && nums[i] <= i) {
6+
continue
7+
}
8+
ans++
9+
}
10+
return
11+
}

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