#530 · #358 · Rearrange String k Distance Apart(K 距离间隔重排字符串)

Given a string s and an integer k, rearrange it so that the same characters are at least k positions apart. Return any valid arrangement, or the empty string if impossible. Constraints: 1 <= s.length <= 3 * 10^4, 0 <= k <= s.length, lowercase letters.