feat(859): finish buddy string

Author: plh97

kit/859.BuddyStrings/README.md

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+# [859. Buddy Strings](https://leetcode.com/problems/buddy-strings/)
+
+## 2019/05/09
+
+### 题目 💗[easy]
+
+A 和 B 两个变量, A 你能够在对调两个字符串后 等于 B 则返回 true ,否则 flase

kit/859.BuddyStrings/main.go

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+package buddyStrings
+
+func buddyStrings(A string, B string) bool {
+	if A == B {
+		for i := range A {
+			if i > 0 && A[i] == A[0] {
+				return true
+			}
+		}
+		return false
+	} else {
+		l, r := 0, len(A)-1
+		for l < r {
+			if A[r] != B[r] && A[l] != B[l] {
+				runeA := []rune(A)
+				runeA[r], runeA[l] = runeA[l], runeA[r]
+				A = string(runeA)
+				break
+			} else {
+				if A[l] == B[l] {
+					l++
+				}
+				if A[r] == B[r] {
+					r--
+				}
+			}
+		}
+	}
+	return A == B
+}