75. Sort Colors

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75. Sort Colors

Description

Given an array nums 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.

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

You must solve this problem without using the library’s sort function.

Example 1:

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Input: nums = [2,0,2,1,1,0]
Output: [0,0,1,1,2,2]

Example 2:

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Input: nums = [2,0,1]
Output: [0,1,2]

Constraints:

  • n == nums.length
  • 1 <= n <= 300
  • nums[i] is either 0, 1, or 2.

Follow up: Could you come up with a one-pass algorithm using only constant extra space?

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    void sortColors(vector<int>& nums) {
        int left = 0, right = nums.size() - 1;
        for (int i = 0; i <= right; i++) {
            if (nums[i] == 0) {
                swap(nums[i], nums[left++]);
            } else if (nums[i] == 2) {
                swap(nums[i], nums[right--]);
                i--;
            }
        }
    }
};