feat: add solutions to lc problem: No.1995

No.1995.Count Special Quadruplets

Author: yanglbme

Diff for: solution/1900-1999/1995.Count Special Quadruplets/README.md

@@ -53,22 +53,234 @@
 
 <!-- 这里可写通用的实现逻辑 -->
 
+直接暴力枚举，或者用哈希表实现。
+
 <!-- tabs:start -->
 
 ### **Python3**
 
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```python
+class Solution:
+    def countQuadruplets(self, nums: List[int]) -> int:
+        ans, n = 0, len(nums)
+        for a in range(n - 3):
+            for b in range(a + 1, n - 2):
+                for c in range(b + 1, n - 1):
+                    for d in range(c + 1, n):
+                        if nums[a] + nums[b] + nums[c] == nums[d]:
+                            ans += 1
+        return ans
+```
 
+```python
+class Solution:
+    def countQuadruplets(self, nums: List[int]) -> int:
+        ans, n = 0, len(nums)
+        counter = Counter()
+        for c in range(n - 2, 1, -1):
+            counter[nums[c + 1]] += 1
+            for a in range(c - 1):
+                for b in range(a + 1, c):
+                    ans += counter[nums[a] + nums[b] + nums[c]]
+        return ans
+```
+
+```python
+class Solution:
+    def countQuadruplets(self, nums: List[int]) -> int:
+        ans, n = 0, len(nums)
+        counter = Counter()
+        for b in range(n - 3, 0, -1):
+            c = b + 1
+            for d in range(c + 1, n):
+                counter[nums[d] - nums[c]] += 1
+            for a in range(b):
+                ans += counter[nums[a] + nums[b]]
+        return ans
 ```
 
 ### **Java**
 
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```java
+class Solution {
+    public int countQuadruplets(int[] nums) {
+        int ans = 0, n = nums.length;
+        for (int a = 0; a < n - 3; ++a) {
+            for (int b = a + 1; b < n - 2; ++b) {
+                for (int c = b + 1; c < n - 1; ++c) {
+                    for (int d = c + 1; d < n; ++d) {
+                        if (nums[a] + nums[b] + nums[c] == nums[d]) {
+                            ++ans;
+                        }
+                    }
+                }
+            }
+        }
+        return ans;
+    }
+}
+```
+
+```java
+class Solution {
+    public int countQuadruplets(int[] nums) {
+        int ans = 0, n = nums.length;
+        int[] counter = new int[310];
+        for (int c = n - 2; c > 1; --c) {
+            ++counter[nums[c + 1]];
+            for (int a = 0; a < c - 1; ++a) {
+                for (int b = a + 1; b < c; ++b) {
+                    ans += counter[nums[a] + nums[b] + nums[c]];
+                }
+            }
+        }
+        return ans;
+    }
+}
+```
+
+```java
+class Solution {
+    public int countQuadruplets(int[] nums) {
+        int ans = 0, n = nums.length;
+        int[] counter = new int[310];
+        for (int b = n - 3; b > 0; --b) {
+            int c = b + 1;
+            for (int d =  c + 1; d < n; ++d) {
+                if (nums[d] - nums[c] >= 0) {
+                    ++counter[nums[d] - nums[c]];
+                }
+            }
+            for (int a = 0; a < b; ++a) {
+                ans += counter[nums[a] + nums[b]];
+            }
+        }
+        return ans;
+    }
+}
+```
+
+### **C++**
+
+```cpp
+class Solution {
+public:
+    int countQuadruplets(vector<int>& nums) {
+        int ans = 0, n = nums.size();
+        for (int a = 0; a < n - 3; ++a)
+            for (int b = a + 1; b < n - 2; ++b)
+                for (int c = b + 1; c < n - 1; ++c)
+                    for (int d = c + 1; d < n; ++d)
+                        if (nums[a] + nums[b] + nums[c] == nums[d]) ++ans;
+        return ans;
+    }
+};
+```
+
+```cpp
+class Solution {
+public:
+    int countQuadruplets(vector<int>& nums) {
+        int ans = 0, n = nums.size();
+        vector<int> counter(310);
+        for (int c = n - 2; c > 1; --c)
+        {
+            ++counter[nums[c + 1]];
+            for (int a = 0; a < c - 1; ++a)
+            {
+                for (int b = a + 1; b < c; ++b)
+                {
+                    ans += counter[nums[a] + nums[b] + nums[c]];
+                }
+            }
+        }
+        return ans;
+    }
+};
+```
+
+```cpp
+class Solution {
+public:
+    int countQuadruplets(vector<int>& nums) {
+        int ans = 0, n = nums.size();
+        vector<int> counter(310);
+        for (int b = n - 3; b > 0; --b)
+        {
+            int c = b + 1;
+            for (int d = c + 1; d < n; ++d)
+            {
+                if (nums[d] - nums[c] >= 0)
+                {
+                    ++counter[nums[d] - nums[c]];
+                }
+            }
+            for (int a = 0; a < b; ++a) {
+                ans += counter[nums[a] + nums[b]];
+            }
+        }
+        return ans;
+    }
+};
+```
+
+### **Go**
+
+```go
+func countQuadruplets(nums []int) int {
+	ans, n := 0, len(nums)
+	for a := 0; a < n-3; a++ {
+		for b := a + 1; b < n-2; b++ {
+			for c := b + 1; c < n-1; c++ {
+				for d := c + 1; d < n; d++ {
+					if nums[a]+nums[b]+nums[c] == nums[d] {
+						ans++
+					}
+				}
+			}
+		}
+	}
+	return ans
+}
+```
+
+```go
+func countQuadruplets(nums []int) int {
+	ans, n := 0, len(nums)
+	counter := make([]int, 310)
+	for c := n - 2; c > 1; c-- {
+		counter[nums[c+1]]++
+		for a := 0; a < c-1; a++ {
+			for b := a + 1; b < c; b++ {
+				ans += counter[nums[a]+nums[b]+nums[c]]
+			}
+		}
+	}
+	return ans
+}
+```
 
+```go
+func countQuadruplets(nums []int) int {
+	ans, n := 0, len(nums)
+	counter := make([]int, 310)
+	for b := n - 3; b > 0; b-- {
+		c := b + 1
+		for d := c + 1; d < n; d++ {
+			if nums[d] >= nums[c] {
+				counter[nums[d]-nums[c]]++
+			}
+		}
+		for a := 0; a < b; a++ {
+			ans += counter[nums[a]+nums[b]]
+		}
+	}
+	return ans
+}
 ```
 
 ### **...**