solve problem Buddy Strings

Author: P-ppc

README.md

@@ -191,6 +191,7 @@ All solutions will be accepted!
 |633|[Sum Of Square Numbers](https://leetcode-cn.com/problems/sum-of-square-numbers/description/)|[java/py/js](./algorithms/SumOfSquareNumbers)|Easy|
 |605|[Can Place Flowers](https://leetcode-cn.com/problems/can-place-flowers/description/)|[java/py/js](./algorithms/CanPlaceFlowers)|Easy|
 |204|[Count Primes](https://leetcode-cn.com/problems/count-primes/description/)|[java/py/js](./algorithms/CountPrimes)|Easy|
+|859|[Buddy Strings](https://leetcode-cn.com/problems/buddy-strings/description/)|[java/py/js](./algorithms/BuddyStrings)|Easy|
 
 # Database
 |#|Title|Solution|Difficulty|

algorithms/BuddyStrings/README.md

@@ -0,0 +1,2 @@
+# Buddy Strings
+This problem is easy to solve

algorithms/BuddyStrings/Solution.java

@@ -0,0 +1,27 @@
+class Solution {
+    public boolean buddyStrings(String A, String B) {
+        if (A.length() != B.length()) return false;
+        
+        if (A.equals(B)) {
+            Map<Character, Boolean> characterMap = new HashMap<Character, Boolean>();
+            for (char c : A.toCharArray()) {
+                if (characterMap.get(c) == null) {
+                    characterMap.put(c, true);
+                } else {
+                    return true;
+                }
+            }
+            return false;
+        } else {
+            List<Character> diffs = new ArrayList<Character>();
+            for (int i = 0; i < A.length(); i++) {
+                if (A.charAt(i) != B.charAt(i)) {
+                    diffs.add(A.charAt(i));
+                    diffs.add(B.charAt(i));
+                }
+            }
+            if (diffs.size() == 4 && diffs.get(0) == diffs.get(3) && diffs.get(1) == diffs.get(2)) return true;
+            return false;
+        }
+    }
+}

algorithms/BuddyStrings/solution.js

@@ -0,0 +1,30 @@
+/**
+ * @param {string} A
+ * @param {string} B
+ * @return {boolean}
+ */
+var buddyStrings = function(A, B) {
+    if (A.length !== B.length) return false
+    
+    if (A === B) {
+        let characterMap = {}
+        for (let i = 0; i < A.length; i++) {
+            if (characterMap[A[i]] === undefined) {
+                characterMap[A[i]] = true
+            } else {
+                return true
+            }
+        }
+        return false
+    } else {
+        let diffs = []
+        for (let i = 0; i < A.length; i++) {
+            if (A[i] !== B[i]) {
+                diffs.push(A[i])
+                diffs.push(B[i])
+            }            
+        }
+        if (diffs.length === 4 && diffs[0] === diffs[3] && diffs[1] == diffs[2]) return true
+        return false
+    }
+};

algorithms/BuddyStrings/solution.py

@@ -0,0 +1,31 @@
+class Solution(object):
+    def buddyStrings(self, A, B):
+        """
+        :type A: str
+        :type B: str
+        :rtype: bool
+        """
+        if len(A) != len(B):
+            return False
+        
+        if A == B:
+            # 只要有一个重复的字母即可
+            character_map = {}
+            for c in A:
+                if character_map.get(c) == None:
+                    character_map[c] = True
+                else:
+                    return True
+            return False
+        else:
+            # 只能有2个位置不同，且a1 == b2 and b1 == a2
+            diffs = []
+            for i in range(len(A)):
+                if A[i] != B[i]:
+                    diffs.append(A[i])
+                    diffs.append(B[i])
+            if len(diffs) == 4 and diffs[0] == diffs[3] and diffs[1] == diffs[2]:
+                return True
+            return False
+            
+