1.1 for (int i=x.length-1; i > 0; i--)没有遍历整个数组， 应该为for (int i=x.length-1; i >= 0; i--) 。
1.2 test: x=[3, 2, 5]; y = 2 。
1.3 test: x=[3, 3, 5]; y = 2 。
1.4 test: x = [ 2 ],y = 2。
2.1 for 循环应改为for(i = x.length -1 ; i >= 0; i--)
2.2 test: x = [0, 2]
2.3 test: x = [2, 0, 0]
2.4 test: x = [0]