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59 lines
2.0 KiB
Markdown
59 lines
2.0 KiB
Markdown
# [895. Maximum Frequency Stack](https://leetcode.com/problems/maximum-frequency-stack/)
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## 题目
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Implement FreqStack, a class which simulates the operation of a stack-like data structure.
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FreqStack has two functions:
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push(int x), which pushes an integer x onto the stack.
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pop(), which removes and returns the most frequent element in the stack.
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If there is a tie for most frequent element, the element closest to the top of the stack is removed and returned.
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Example 1:
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```c
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Input:
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["FreqStack","push","push","push","push","push","push","pop","pop","pop","pop"],
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[[],[5],[7],[5],[7],[4],[5],[],[],[],[]]
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Output: [null,null,null,null,null,null,null,5,7,5,4]
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Explanation:
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After making six .push operations, the stack is [5,7,5,7,4,5] from bottom to top. Then:
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pop() -> returns 5, as 5 is the most frequent.
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The stack becomes [5,7,5,7,4].
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pop() -> returns 7, as 5 and 7 is the most frequent, but 7 is closest to the top.
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The stack becomes [5,7,5,4].
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pop() -> returns 5.
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The stack becomes [5,7,4].
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pop() -> returns 4.
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The stack becomes [5,7].
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```
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Note:
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- Calls to FreqStack.push(int x) will be such that 0 <= x <= 10^9.
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- It is guaranteed that FreqStack.pop() won't be called if the stack has zero elements.
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- The total number of FreqStack.push calls will not exceed 10000 in a single test case.
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- The total number of FreqStack.pop calls will not exceed 10000 in a single test case.
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- The total number of FreqStack.push and FreqStack.pop calls will not exceed 150000 across all test cases.
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## 题目大意
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实现 FreqStack，模拟类似栈的数据结构的操作的一个类。
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FreqStack 有两个函数：
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- push(int x)，将整数 x 推入栈中。
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- pop()，它移除并返回栈中出现最频繁的元素。如果最频繁的元素不只一个，则移除并返回最接近栈顶的元素。
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## 解题思路
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FreqStack 里面保存频次的 map 和相同频次 group 的 map。push 的时候动态的维护 x 的频次，并更新到对应频次的 group 中。pop 的时候对应减少频次字典里面的频次，并更新到对应频次的 group 中。
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