现有n个红白蓝三种不同颜色的小球，乱序排列在一起，请通过两两交换任意两个球，使得从左至右，依次是一些红球、一些白球、一些蓝球。
public class DutchNationalFlag {
private void swap(int[] a, int index1, int index2) {
int temp = a[index1];
a[index1] = a[index2];
a[index2] = temp;
}
public void dutchNationalFlag(int[] a, int n) {
//红色游标
int left = 0;
//蓝色游标
int right = n - 1;
//白色游标
int cur = 1;
while (cur <= right) {
if (a[cur] == 0) { //红色
swap(a, left, cur);
left++;
} else if (a[cur] == 1) { //白色
cur++;
} else { //蓝色
swap(a, cur, right);
right--;
}
}
}
public static void main(String[] args) {
int[] a = { 0, 1, 1, 2, 2, 2, 0, 0, 0, 1, 1 };
DutchNationalFlag dFlag = new DutchNationalFlag();
dFlag.dutchNationalFlag(a, a.length);
for (int value : a) {
System.out.print(value);
System.out.print(" ");
}
}
}
