leetcode SortColors
z
 2019-04-09 10:36:27   
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
public class SortColors {
    public void sortColors(int[] nums) {
        /**
         * Given an array with n objects colored red, white or blue, sort them in-place 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.
         *
         * Example:
         *
         * Input: [2,0,2,1,1,0]
         * Output: [0,0,1,1,2,2]
         * Follow up:
         *
         * A rather straight forward solution is a two-pass algorithm using counting sort.
         * First, iterate the array counting number of 0's, 1's, and 2's, then overwrite array with total number of 0's,
         * then 1's and followed by 2's.
         * Could you come up with a one-pass algorithm using only constant space?
         */
        int left = 0;
        int right = nums.length-1;
        int i = 0;
        while (i<=right) {
            if (nums[i] == 2) {
                swap(nums, i, right);
                right --;
            }
            else if (nums[i] == 0) {
                swap(nums, i, left);
                left ++;
            }
            else
                i ++;
        }
    }
    public void swap(int[] nums, int i, int j) {
        int t= nums[i];
        nums[i] = nums[j];
        nums[j] = t;
    }
}