【LeetCode】75. Sort Colors

問題描述

https://leetcode.com/problems/sort-colors/#/description

Given an array with n objects colored red, white or blue, sort them so that objects of the same color are adjacent, with the colors in the order red, white and blue.

Here, we will use the integers 0, 1, and 2 to represent the color red, white, and blue respectively.

Note:
You are not suppose to use the library’s sort function for this problem.

算法

因爲只有3個不同的元素，所以計數排序即可
首先迭代記錄0,1,2一共各有多少個數，然後按照0,1,2的順序依次填充到數組中即可。

代碼

        public void sortColors(int[] nums) {
            int[] cnt = new int[3];
            for(int i=0;i<nums.length;i++) {
                cnt[nums[i]]++;
            }
            for(int i=0,j=0;i<nums.length;i++,cnt[j]--) {
                while(cnt[j]==0) {
                    j++;
                }
                nums[i] = j;
            }
        }