【堆】 LeetCode215. 数组中的第K个最大元素

港控/mmm° 2022-12-03 09:20 191阅读 0赞

### 题目 ###

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE3MjYwMDU_size_16_color_FFFFFF_t_70_pic_center]

### 解答 ###

#include <iostream>
    #include <string>
    #include <list>
    #include <vector>
    #include <queue>
    #include <functional>
    #include <cassert>
    
    // 215. Kth Largest Element in an Array
    
    // 数据结构堆得巧用。
    
    // 使用堆得效率特别高。
    int findKthLargest(std::vector<int>& nums, int k) { 
      std::priority_queue<int, std::vector<int>, std::greater<int>> min_heap;
      for (int num : nums) { 
        if (min_heap.size() < k) { 
          min_heap.push(num);
          continue;
        }
    
        if (min_heap.top() < num) { 
          min_heap.pop();
          min_heap.push(num);
        }
      }
    
      return min_heap.top();
    }
    
    // 这种排序的方法十分耗时。
    int findKthLargest2(std::vector<int>& nums, int k) { 
      std::vector<int> temp_nums = nums;
      std::size_t nums_len = temp_nums.size();
    
      for (int i = 0; i < k; ++i) { 
        for (int j = i + 1; j < nums_len; ++ j) { 
          if (temp_nums[i] < temp_nums[j]) { 
            std::swap(temp_nums[i], temp_nums[j]);
          }
        }
      }
    
      return temp_nums[k - 1];
    }
    
    int main() { 
      std::vector<int> nums = {  1, 2, -4, 7, 10, 3, 4 };
      std::cout << findKthLargest(nums, 2) << std::endl;
      std::cout << findKthLargest(nums, 1) << std::endl;
      std::cout << findKthLargest(nums, 3) << std::endl;
    
      std::cout << "=========================================" << std::endl;
    
      std::cout << findKthLargest2(nums, 2) << std::endl;
      std::cout << findKthLargest2(nums, 1) << std::endl;
      std::cout << findKthLargest2(nums, 3) << std::endl;
    
      return 0;
    }

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