LeetCode [895] Maximum Frequency Stack

Implement FreqStack, a class which simulates the operation of a stack-like data structure.

FreqStack has two functions:

• push(int x), which pushes an integer x onto the stack.
• pop(), which removes and returns the most frequent element in the stack.
  • If there is a tie for most frequent element, the element closest to the top of the stack is removed and returned.

Example 1:

Input: 
["FreqStack","push","push","push","push","push","push","pop","pop","pop","pop"],
[[],[5],[7],[5],[7],[4],[5],[],[],[],[]]
Output: [null,null,null,null,null,null,null,5,7,5,4]
Explanation:
After making six .push operations, the stack is [5,7,5,7,4,5] from bottom to top.  Then:

pop() -> returns 5, as 5 is the most frequent.
The stack becomes [5,7,5,7,4].

pop() -> returns 7, as 5 and 7 is the most frequent, but 7 is closest to the top.
The stack becomes [5,7,5,4].

pop() -> returns 5.
The stack becomes [5,7,4].

pop() -> returns 4.
The stack becomes [5,7].

Note:

• Calls to FreqStack.push(int x) will be such that 0 <= x <= 10^9.
• It is guaranteed that FreqStack.pop() won't be called if the stack has zero elements.
• The total number of FreqStack.push calls will not exceed 10000 in a single test case.
• The total number of FreqStack.pop calls will not exceed 10000 in a single test case.
• The total number of FreqStack.push and FreqStack.pop calls will not exceed 150000 across all test cases.

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struct Ele{ int value; int index; int count; Ele(int v, int i, int c):value(v),index(i),count(c){} }; struct Comp { bool operator()(const Ele& lhs, const Ele& rhs) { if (lhs.count<rhs.count) return true; if (lhs.count==rhs.count) return lhs.index<rhs.index; return false; } }; class FreqStack { priority_queue<Ele, vector<Ele>, Comp> pq; int index = 0; map<int, int> mp;//number, count public: FreqStack() { } void push(int x) { Ele e(x, index++, ++mp[x]); pq.push(e); } int pop() { int v = pq.top().value; pq.pop(); mp[v]--; return v; } }; /** * Your FreqStack object will be instantiated and called as such: * FreqStack* obj = new FreqStack(); * obj->push(x); * int param_2 = obj->pop(); */