刷題581. Shortest Unsorted Continuous Subarray

一、題目說明

題目581. Shortest Unsorted Continuous Subarray，求最大連續子數組（如果該子數組有序，則整個數組有序）的長度。難度是Easy！

二、我的解答

不動腦子，將數組排序，然後從左到右比較，再從右到左比較。即可獲得最短子數組的長度。

class Solution{
	public:
		int findUnsortedSubarray(vector<int>& nums){
			int len = nums.size()-1;
			vector<int> tmp;
			for(int i=0;i<nums.size();i++){
				tmp.push_back(nums[i]);
			}
			sort(tmp.begin(),tmp.end());
			int left = 0,right = len;
			while(left<len && tmp[left]==nums[left]){
				left++;
			}
			while(right>=left && tmp[right]==nums[right]){
				right--;
			}
			return (right-left+1);
		}
};

性能如下：

Runtime: 44 ms, faster than 51.61% of C++ online submissions for Shortest Unsorted Continuous Subarray.
Memory Usage: 11.3 MB, less than 38.10% of C++ online submissions for Shortest Unsorted Continuous Subarray.

三、優化措施

優化如下：

class Solution{
	public:
		int findUnsortedSubarray(vector<int>& nums){
			int m = nums[0], n = nums.back(), l = -1, r = -2;
	        int len = nums.size();
	        //從左到右遍歷，如果nums[i]比前面的都大，則i+1的位置正確 
	        for (int i = 1; i < len; ++i)
	        {
	            m = max(m, nums[i]);
	            n = min(n, nums[len - 1 - i]);
	            if (m != nums[i]) r = i;
	            if (n != nums[len - 1 - i]) l = len - 1 - i;
	        }
	        return r - l + 1;
		}
};

性能如下：

Runtime: 36 ms, faster than 77.82% of C++ online submissions for Shortest Unsorted Continuous Subarray.
Memory Usage: 10.5 MB, less than 71.43% of C++ online submissions for Shortest Unsorted Continuous Subarray.