# 3.07.2023 [859. Buddy Strings]

Is it just one swap `s[i]<>s[j]` to string `s` == string `goal`

3.07.2023

859. Buddy Strings easy
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Problem TLDR

Is it just one swap s[i]<>s[j] to string s == string goal

Intuition

Compare two strings for each position. There are must be only two not equal positions and they must be mirrored pairs.

Approach

Let’s write it in Kotlin collections API style.

Complexity

• Time complexity:
  O(n)

• Space complexity:
  O(n)

Code

fun buddyStrings(s: String, goal: String): Boolean = s.length == goal.length && (
s == goal && s.groupBy { it }.any { it.value.size > 1 } ||
s.zip(goal)
.filter { (a, b) -> a != b }
.windowed(2)
.map { (ab, cd) -> listOf(ab, cd.second to cd.first) }
.let { it.size == 1 && it[0][0] == it[0][1] }
)