Sort Colors

ID: 75; medium

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Solution 1 (Go)

func sortColors(nums []int)  {
    j := 0
    for i := 0; i < len(nums); i++ {
        if nums[i] == 0 {
            nums[i], nums[j] = nums[j], nums[i]
            j++
        }
    }
    
    for i := j; i < len(nums); i++ {
        if nums[i] == 1 {
            nums[i], nums[j] = nums[j], nums[i]
            j++
        }
    }
}

Solution 2 (Go)

func sortColors(nums []int)  {
    i, j, k := 0, 0, len(nums)-1
    for j <= k {
        if nums[j] == 0 {
            nums[i], nums[j] = nums[j], nums[i]
            i++
            j++
        } else if nums[j] == 1 {
            j++
        } else {
            nums[j], nums[k] = nums[k], nums[j]
            k--
        }
    }
}

[0, i): the interval containing all 0's

[i, j): the interval containing all 1's

[j ,k): the interval to be explored

[k ,len(nums)): the interval containing all 2's

Solution 3 (Java)

public class Solution {
    /**
     * @param nums: A list of integer which is 0, 1 or 2 
     * @return: nothing
     */
    public void sortColors(int[] nums) {
        quickSort(nums, 1);
        quickSort(nums, 2);
    }

    private void quickSort(int[] nums, int k) {
        if (nums == null) return;
        int i = 0, j = nums.length - 1;
        while (i <= j) {
            while (i <= j && nums[i] < k) {
                i++;
            }
            while (i <= j && nums[j] >= k) {
                j--;
            }
            if (i <= j) {
                int temp = nums[i];
                nums[i] = nums[j];
                nums[j] = temp;
            }
        }
    }
}

Notes

• Quick sort

Solution 4 (Java)

public class Solution {
    /**
     * @param nums: A list of integer which is 0, 1 or 2 
     * @return: nothing
     */
    public void sortColors(int[] nums) {
        Arrays.sort(nums);
    }
}

Notes

• Not really a "solution"...

Solution 5 (Java)

public class Solution {
    /**
     * @param nums: A list of integer which is 0, 1 or 2 
     * @return: nothing
     */
    public void sortColors(int[] nums) {
        int i = 0, j = 0, k = nums.length - 1;
        while (j <= k) {
            if (nums[j] == 0) {
                swap(nums, j, i);
                i++;
                j++;
            } else if (nums[j] == 1) {
                j++;
            } else {
                swap(nums, j, k);
                k--;
            }
        }
    }

    private void swap(int[] nums, int a, int b) {
        int temp = nums[a];
        nums[a] = nums[b];
        nums[b] = temp;
    }
}

// [0, i) all 0's
// [i, j) all 1's
// [j, k) exploring
// [k, nums.length - 1) all 2's

Notes

• Same as Solution 2 but in Java.