LeetCode:Sort Colors

題目連接

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.

 

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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分析：題目說了一大堆，就是讓對一個數組排序，數組中的元素只有0、一、2，而且要求只能遍歷一遍數組，常數空間複雜度。藉助於快速排序的partition思想，以1爲樞紐元對數組進行劃分，使0在數組的左邊，2在數組的右邊，1在數組的中間。                                           本文地址

class Solution {
public:
    void sortColors(int A[], int n) {
        //zeroEnd是放0那部分的尾部索引，twoEnd是放2那部分的首部索引
        //碰到0放到zeroEnd+1處，碰到2放到twoEnd-1處，碰到1指針後移
        int zeroEnd = -1, twoBegin = n, i = 0;
        while(i < twoBegin)
        {
            if(A[i] == 0 && i != ++zeroEnd)
                swap(A[zeroEnd], A[i]);
            else if(A[i] == 2 && i != --twoBegin)
                swap(A[twoBegin], A[i]);
            else
                i++;
        }
    }
};

 

【版權聲明】轉載請註明出處：http://www.cnblogs.com/TenosDoIt/p/3464360.html