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leetcode--Sort Colors

2024-07-07 09:00:23   224人阅读

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.

click to show follow up.

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 an one-pass algorithm using only constant space?

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public class Solution {
    /**This is a fundamental problem.<br>
     * Since we know the possible numbers in the array and know where we should put them,
     * we can sort them in O(n) time.
     *
     * @param A --Integer array, the array contains 0‘s , 1‘s , 2‘s.
     * @author Averill Zheng
     * @version 2014-06-05
     * @since JDk 1.7
     */
    public void sortColors(int[] A) {
        int length = A.length, tail = length, head = 0;
         
        for(int i = 0; i < tail; ++i){
            if(A[i] == 0){
                int temp = A[head];
                A[head] = A[i];
                ++head;
                A[i] = temp;
            }
            else if(A[i] == 2){
                int temp = A[tail - 1];
                A[tail - 1] = A[i];
                A[i] = temp;
                --tail;
                --i;
            }
        }   
    }
}

　　


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