feat: add python and java solutions to lcci problem: No.16.21

添加《程序员面试金典》题解：面试题 16.21. 交换和

Author: yanglbme

Diff for: lcci/16.21.Sum Swap/README.md

@@ -28,20 +28,51 @@
 
 ## 解法
 <!-- 这里可写通用的实现逻辑 -->
-
+先计算两个数组的差值 `diff`，若 `diff` 为奇数，则说明无满足条件的数值，返回空数组。否则，将 `array2` 转为 `set`。然后遍历 `array1` 中的每个数 `e`，若值 `e - diff` 在 `set` 中，则说明找到满足条件的数值对。
 
 ### Python3
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```python
-
+class Solution:
+    def findSwapValues(self, array1: List[int], array2: List[int]) -> List[int]:
+        diff = sum(array1) - sum(array2)
+        if diff & 1: return []
+        diff >>= 1
+        s = set(array2)
+        for e in array1:
+            if (e - diff) in s: return [e, e - diff]
+        return []
 ```
 
 ### Java
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```java
-
+class Solution {
+    public int[] findSwapValues(int[] array1, int[] array2) {
+        int diff = sum(array1) - sum(array2);
+        if ((diff & 1) == 1) {
+            return new int[]{};
+        }
+        diff >>= 1;
+        Set<Integer> s = Arrays.stream(array2).boxed().collect(Collectors.toSet());
+        for (int e : array1) {
+            if (s.contains((e - diff))) {
+                return new int[]{e, e - diff};
+            }
+        }
+        return new int[]{};
+    }
+
+    private int sum(int[] array) {
+        int res = 0;
+        for (int e : array) {
+            res += e;
+        }
+        return res;
+    }
+}s
 ```
 
 ### ...

Diff for: lcci/16.21.Sum Swap/README_EN.md

@@ -54,13 +54,44 @@
 ### Python3
 
 ```python
-
+class Solution:
+    def findSwapValues(self, array1: List[int], array2: List[int]) -> List[int]:
+        diff = sum(array1) - sum(array2)
+        if diff & 1: return []
+        diff >>= 1
+        s = set(array2)
+        for e in array1:
+            if (e - diff) in s: return [e, e - diff]
+        return []
 ```
 
 ### Java
 
 ```java
-
+class Solution {
+    public int[] findSwapValues(int[] array1, int[] array2) {
+        int diff = sum(array1) - sum(array2);
+        if ((diff & 1) == 1) {
+            return new int[]{};
+        }
+        diff >>= 1;
+        Set<Integer> s = Arrays.stream(array2).boxed().collect(Collectors.toSet());
+        for (int e : array1) {
+            if (s.contains((e - diff))) {
+                return new int[]{e, e - diff};
+            }
+        }
+        return new int[]{};
+    }
+
+    private int sum(int[] array) {
+        int res = 0;
+        for (int e : array) {
+            res += e;
+        }
+        return res;
+    }
+}
 ```
 
 ### ...

Diff for: lcci/16.21.Sum Swap/Solution.java

@@ -0,0 +1,24 @@
+class Solution {
+    public int[] findSwapValues(int[] array1, int[] array2) {
+        int diff = sum(array1) - sum(array2);
+        if ((diff & 1) == 1) {
+            return new int[]{};
+        }
+        diff >>= 1;
+        Set<Integer> s = Arrays.stream(array2).boxed().collect(Collectors.toSet());
+        for (int e : array1) {
+            if (s.contains((e - diff))) {
+                return new int[]{e, e - diff};
+            }
+        }
+        return new int[]{};
+    }
+
+    private int sum(int[] array) {
+        int res = 0;
+        for (int e : array) {
+            res += e;
+        }
+        return res;
+    }
+}

Diff for: lcci/16.21.Sum Swap/Solution.py

@@ -0,0 +1,9 @@
+class Solution:
+    def findSwapValues(self, array1: List[int], array2: List[int]) -> List[int]:
+        diff = sum(array1) - sum(array2)
+        if diff & 1: return []
+        diff >>= 1
+        s = set(array2)
+        for e in array1:
+            if (e - diff) in s: return [e, e - diff]
+        return []