leetcode75

class Solution {
public:
    void sortColors(vector<int>& nums) {
        sort(nums.begin(), nums.end());
    }
};

 上面这个太弱了，给一个强不了多少的

class Solution:    
    def sortColors(self, nums: 'List[int]') -> 'None':
        red = 0
        white = 0
        blue = 0
        for n in nums:
            if n == 0:
                red+=1
            elif n == 1:
                white += 1
            elif n == 2:
                blue += 1
            else:
                print('error')
        nums.clear()
        nums.extend([0]*red + [1]*white + [2]*blue)

下面给出一个比较强的

class Solution:    
    def swap(self,nums,i,j):
        nums[i],nums[j] = nums[j],nums[i]
        '''
        temp = nums[i]
        nums[i] = nums[j]
        nums[j] = temp
        '''

    def sortColors(self, nums: 'List[int]') -> 'None':
        n = len(nums)
        left = 0
        right = n - 1
        i = 0
        while i <= right:
            if nums[i] == 0:
                if i != left:
                    self.swap(nums,i,left)
                i += 1
                left += 1
            elif nums[i] == 1:
                i += 1
            else:
                self.swap(nums,i,right)

注意swap的写法，如果用temp来存，速度会慢很多。