Poison

75. Sort Colors

发表于
Swap
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
class Solution {
    public void sortColors(int[] nums) {
        int orderedIndex = -1;

        for (int i = orderedIndex + 1; i < nums.length; i++) {
            if (nums[i] == 0) {
                swap(nums, i, ++orderedIndex);
            }
        }

        for (int i = orderedIndex + 1; i < nums.length; i++) {
            if (nums[i] == 1) {
                swap(nums, i, ++orderedIndex);
            }
        }
    }

    private void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }
}
Swap
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
class Solution {
    public void sortColors(int[] nums) {
        int zeroEndIndex = 0, oneEndIndex = 0, twoEndIndex = 0;

        for (int i = 0; i < nums.length; i++) {
            if (nums[i] == 2) {
                nums[twoEndIndex++] = 2;
            } else if (nums[i] == 1) {
                nums[twoEndIndex++] = 2;
                nums[oneEndIndex++] = 1;
            } else {
                nums[twoEndIndex++] = 2;
                nums[oneEndIndex++] = 1;
                nums[zeroEndIndex++] = 0;
            }
        }
    }
}
Swap
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
class Solution {
    public void sortColors(int[] nums) {
        // ordered:
        // 0: [0, left - 1]
        // 2: [right + 1, nums.length - 1]
        int left = 0, right = nums.length - 1; // 下一个填入 0 的索引，下一个填入 2 的索引

        int i = 0;
        while (i <= right) {
            if (nums[i] == 0) {
                swap(nums, i++, left++);
            } else if (nums[i] == 2) {
                // 交换至 nums[i] 的值可能为 0, 1, 2, 所以不推进 i 索引，而是要根据具体的值重新进入 while 循环继续处理
                swap(nums, i, right--);
            } else {
                // nums[i] == 1
                i++;
            }
        }
    }

    private void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }
}
Reference

75. Sort Colors