[leetcode 75] Sort Colors

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.

class Solution {public:    void sortColors(int A[], int n) {        if (n == 1) {            return ;        }        int first = 0;        int last = n-1;        while (first <= last) {            while (first < last && A[first] == 0) {                first++;            }            while (last > first && A[last] != 0) {                last--;            }            swap(A[first], A[last]);            first++;            last--;        }        first = 0;        last = n - 1;        while (first <= last) {            while (first < last && A[first] < 2) {                first++;            }            while (last > first && A[last] == 2) {                last--;            }            swap(A[first], A[last]);            first++;            last--;        }    }};

思路2： 用两个index分别记录红色和蓝色的位置

class Solution {public:    void sortColors(int A[], int n) {        if (n == 1) {            return ;        }        int red = 0;        int blue = n - 1;        for (int i = 0; i < blue + 1;) {            if (A[i] == 0) {                swap(A[i++], A[red++]);            } else if (A[i] == 2) {                swap(A[i], A[blue--]);            } else {                i++;            }        }    }};