1+ package hard
2+ 3+ import HashTableTopic
4+ import StackTopic
5+ import java.util.*
6+ 7+ 8+ /* *
9+ * 895. Maximum Frequency Stack
10+ * https://leetcode.com/problems/maximum-frequency-stack/
11+ *
12+ Design a stack-like data structure to push elements to the stack and pop the most frequent element from the stack.
13+ Implement the FreqStack class:
14+ FreqStack() constructs an empty frequency stack.
15+ void push(int val) pushes an integer val onto the top of the stack.
16+ int pop() removes and returns the most frequent element in the stack.
17+ If there is a tie for the most frequent element, the element closest to the stack's top is removed and returned.
18+ BULLSHIT
19+ */
20+ 21+ class Hard895 : HashTableTopic , StackTopic {
22+ 23+ class FreqStack {
24+ var freq: MutableMap <Int , Int > = HashMap ()
25+ var group: MutableMap <Int , Stack <Int >> = HashMap ()
26+ var maxfreq: Int = 0
27+ 28+ fun push (x : Int ) {
29+ val f = freq.getOrDefault(x, 0 ) + 1
30+ freq[x] = f
31+ if (f > maxfreq) maxfreq = f
32+ group.computeIfAbsent(f) { z: Int -> Stack <Int >() }.push(x)
33+ }
34+ 35+ fun pop (): Int {
36+ val x = group[maxfreq]!! .pop()
37+ freq[x] = freq[x]!! - 1
38+ if (group[maxfreq]!! .size == 0 ) maxfreq--
39+ return x
40+ }
41+ }
42+ }
43+ 44+ fun main () {
45+ val stack = Hard895 .FreqStack ()
46+ stack.push(5 )
47+ stack.push(7 )
48+ stack.push(5 )
49+ stack.push(7 )
50+ stack.push(4 )
51+ stack.push(5 )
52+ 53+ println (stack.pop()) // 5
54+ println (stack.pop()) // 7
55+ println (stack.pop()) // 5
56+ println (stack.pop()) // 4
57+ }
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