169. Majority Element

Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times.

You may assume that the array is non-empty and the majority element always exist in the array.

语言:java

1常规思路:

  1.1 建立TreeMap,计算出每个元素的出现频次

1.2 统计出现次数最多的,达到要求(n/2)就返回

缺点:大家都能想到的,效率固然不高。

代码如下:

public int majorityElement(int[] nums) {
        TreeMap<Integer,Integer> map=new TreeMap<Integer,Integer>();
        for(int i=0;i<nums.length;i++)
        {
        	if(map.containsKey(nums[i]))
        	{
        		int curCount = map.get(nums[i]);
        		map.remove(nums[i]);
        		map.put(nums[i], (curCount+1));
        	}
        	else
        		map.put(nums[i], 1);
        }

        for(Map.Entry<Integer,Integer> entry : map.entrySet()) {
        		Integer key = entry.getKey();
        		Integer value = entry.getValue();
        		if(value>nums.length/2)
        			return key;
        }
        return 0;
}


思路2

1 对数组进行排序

2 不管主要元素起点在开头、中间任意位置,索引为n/2的元素一定为主要元素(像是脑筋急转弯)

代码如下:

public int majorityElement(int[] nums) {
       Arrays.sort(nums);
       return nums[nums.length/2];
    }



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