Sort Colors

用双index从头尾两方向同时遍历

public class Solution {
    public void sortColors(int[] A) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        int frontRunner = 0;
        int backRunner = A.length - 1;
        int i = 0;
        while(i < backRunner+1)
        {
            if(A[i] == 0)
            {
                swap(A, frontRunner, i);
                frontRunner++;
                i++;
            }
            else if(A[i] == 1)
                i++;
            else{
                swap(A, backRunner, i);
                backRunner--;
            }
        }
        
    }
    
    private void swap(int[] matrix, int x, int y)
    {
        int tmp = matrix[x];
        matrix[x] = matrix[y];
        matrix[y] = tmp;
    }
}