LeetCode Largest Number JAVA 快速排序

public String largestNumber(int[] num) {

Integer[] a = new Integer[num.length];

for(int i = 0; i < num.length; ++i) a[i] = num[i];

//Arrays.sort(a, new Cmp());
QSort(a, 0, a.length-1);

String s = "";
for(int i = a.length - 1; i >= 0; --i)
s += Integer.toString(a[i]);
int len = s.length();
int i = 0;
while(i < len - 1 && s.charAt(i) == '0') i++;
return s.substring(i);
}

// 快速排序
private void QSort(Integer[] num, int i, int j) {
// TODO Auto-generated method stub
if(i >= j) return;

int key = num[i];
int l = i, r = j;
while( l < r ) {
while(l < r && Bigger(num[r], key)) r--;
if(l < r)
num[l++] = num[r];
while(l < r && Bigger(key, num[l])) l++;
if(l < r)
num[r--] = num[l];
}
num[l] = key;
QSort(num, i, l-1);
QSort(num, l+1, j);
}

// 比较大小函数
private boolean Bigger(int i, int j) {
// TODO Auto-generated method stub
String m = Integer.toString(i) + Integer.toString(j);
String n = Integer.toString(j) + Integer.toString(i);
return m.compareTo(n) >= 0;
}

// 自定义比较类
class Cmp implements Comparator<Integer>
{

@Override
public int compare(Integer o1, Integer o2) {
String m = Integer.toString(o1) + Integer.toString(o2);
String n = Integer.toString(o2) + Integer.toString(o1);
return m.compareTo(n) >= 0 ? 1 : -1;
}

}