leetCode刷题记录 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.

思路：排序题，但是要O（n）复杂度。 可以用直接交换

下面是两种解决方案

package lintcode;

public class SortColors {

public static void main(String[] args) {

int[] nums = new int[]{0,1,2,1,1,2,1,0,1,1};
sortColors2(nums);
}

//方法一
public static void sortColors(int[] nums) {
int r=0, w=0; // label the end of different colors;
for(int num: nums){
if(num == 0) {
nums[w++]=1;
nums[r++]=0;
}
else if(num==1)
nums[w++]=1;
}
for (int i = w; i < nums.length;++i)
nums[i] = 2;
}

//方法二
public static void sortColors2(int[] A) {
int n = A.length;
int second=n-1, zero=0;
for (int i=0; i<=second; i++) {
while (A[i]==2 && i<second) swap(A, i, second--);
while (A[i]==0 && i>zero) swap(A, i, zero++);
}
}

private static void swap(int[] A, int i, int j){
int temp = A[i];
A[i] = A[j];
A[j] = temp;
}
}