feat: add solutions to leetcode problem: No.0447. Number of Boomerangs

Author: yanglbme

solution/0300-0399/0356.Line Reflection/README.md

@@ -47,7 +47,7 @@
 
 先找出所有点中的最小、最大的 x 坐标 `minX` 和 `maxX`。若存在满足条件的直线，则直线 `x = (minX + maxX) / 2`。(或者说：`s = minX + maxX`)
 
-遍历每个点 `point(x, y)`，若 (s - x, y) 不在点集里，说明不满足条件，直接返回 false。遍历结束返回 true。
+遍历每个点 `point(x, y)`，若 `(s - x, y)` 不在点集里，说明不满足条件，直接返回 false。遍历结束返回 true。
 
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solution/0400-0499/0447.Number of Boomerangs/README.md

@@ -45,27 +45,70 @@
 	<li>所有点都 <strong>互不相同</strong></li>
 </ul>
 
-
 ## 解法
 
 <!-- 这里可写通用的实现逻辑 -->
 
+计数器实现。
+
+对于每个点，计算其他点到该点的距离，然后按照距离进行分组计数。对每个组中的点进行两两排列组合（A n 取 2，即 `n * (n - 1))`）计数即可。
+
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 ### **Python3**
 
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```python
-
+class Solution:
+    def numberOfBoomerangs(self, points: List[List[int]]) -> int:
+        n = len(points)
+        if len(points) < 3:
+            return 0
+        number = 0
+        for i in range(n):
+            distance_counter = collections.Counter()
+            for j in range(n):
+                if i == j:
+                    continue
+                x1, y1 = points[i][0], points[i][1]
+                x2, y2 = points[j][0], points[j][1]
+                distance = (x1 - x2) ** 2 + (y1 - y2) ** 2
+                distance_counter[distance] += 1
+            number += sum([val * (val - 1) for val in distance_counter.values()])
+        return number
 ```
 
 ### **Java**
 
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```java
-
+class Solution {
+    public int numberOfBoomerangs(int[][] points) {
+        int n = points.length;
+        if (n < 3) {
+            return 0;
+        }
+        int number = 0;
+        for (int i = 0; i < n; ++i) {
+            Map<Integer, Integer> distanceCounter = new HashMap<>();
+            for (int j = 0; j < n; ++j) {
+                if (i == j) {
+                    continue;
+                }
+                int x1 = points[i][0], y1 = points[i][1];
+                int x2 = points[j][0], y2 = points[j][1];
+                int distance = (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
+                distanceCounter.put(distance, distanceCounter.getOrDefault(distance, 0) + 1);
+            }
+            for (int val : distanceCounter.values()) {
+                number += val * (val - 1);
+            }
+        }
+        return number;
+    }
+}
 ```
 
 ### **...**

solution/0400-0499/0447.Number of Boomerangs/README_EN.md

@@ -50,13 +50,53 @@
 ### **Python3**
 
 ```python
-
+class Solution:
+    def numberOfBoomerangs(self, points: List[List[int]]) -> int:
+        n = len(points)
+        if len(points) < 3:
+            return 0
+        number = 0
+        for i in range(n):
+            distance_counter = collections.Counter()
+            for j in range(n):
+                if i == j:
+                    continue
+                x1, y1 = points[i][0], points[i][1]
+                x2, y2 = points[j][0], points[j][1]
+                distance = (x1 - x2) ** 2 + (y1 - y2) ** 2
+                distance_counter[distance] += 1
+            number += sum([val * (val - 1) for val in distance_counter.values()])
+        return number
 ```
 
 ### **Java**
 
 ```java
-
+class Solution {
+    public int numberOfBoomerangs(int[][] points) {
+        int n = points.length;
+        if (n < 3) {
+            return 0;
+        }
+        int number = 0;
+        for (int i = 0; i < n; ++i) {
+            Map<Integer, Integer> distanceCounter = new HashMap<>();
+            for (int j = 0; j < n; ++j) {
+                if (i == j) {
+                    continue;
+                }
+                int x1 = points[i][0], y1 = points[i][1];
+                int x2 = points[j][0], y2 = points[j][1];
+                int distance = (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
+                distanceCounter.put(distance, distanceCounter.getOrDefault(distance, 0) + 1);
+            }
+            for (int val : distanceCounter.values()) {
+                number += val * (val - 1);
+            }
+        }
+        return number;
+    }
+}
 ```
 
 ### **...**

solution/0400-0499/0447.Number of Boomerangs/Solution.java

@@ -0,0 +1,25 @@
+class Solution {
+    public int numberOfBoomerangs(int[][] points) {
+        int n = points.length;
+        if (n < 3) {
+            return 0;
+        }
+        int number = 0;
+        for (int i = 0; i < n; ++i) {
+            Map<Integer, Integer> distanceCounter = new HashMap<>();
+            for (int j = 0; j < n; ++j) {
+                if (i == j) {
+                    continue;
+                }
+                int x1 = points[i][0], y1 = points[i][1];
+                int x2 = points[j][0], y2 = points[j][1];
+                int distance = (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
+                distanceCounter.put(distance, distanceCounter.getOrDefault(distance, 0) + 1);
+            }
+            for (int val : distanceCounter.values()) {
+                number += val * (val - 1);
+            }
+        }
+        return number;
+    }
+}

solution/0400-0499/0447.Number of Boomerangs/Solution.py

@@ -0,0 +1,17 @@
+class Solution:
+    def numberOfBoomerangs(self, points: List[List[int]]) -> int:
+        n = len(points)
+        if len(points) < 3:
+            return 0
+        number = 0
+        for i in range(n):
+            distance_counter = collections.Counter()
+            for j in range(n):
+                if i == j:
+                    continue
+                x1, y1 = points[i][0], points[i][1]
+                x2, y2 = points[j][0], points[j][1]
+                distance = (x1 - x2) ** 2 + (y1 - y2) ** 2
+                distance_counter[distance] += 1
+            number += sum([val * (val - 1) for val in distance_counter.values()])
+        return number