Homework_2

一、错误代码：

public int findLast (int[] x, int y) 
{ 
//Effects: If x==null throw NullPointerException 
// else return the index of the last element 
// in x that equals y. 
// If no such element exists, return -1 
for (int i=x.length-1; i > 0; i--) 
{
 if (x[i] == y)
 {
 return i;
 } 
}
return -1; 
}
// test: x=[2, 3, 5]; y = 2 
// Expected = 0

回答：

1.检测不到x[0]

2.令x = NULL

3.x = [2,3]; y = 3

4.x = [2,3]; y = 1

二、错误代码

public static int lastZero (int[] x) 
{
 //Effects: if x==null throw NullPointerException
 // else return the index of the LAST 0 in x.
 // Return -1 if 0 does not occur in x
 for (int i = 0; i < x.length; i++) 
{
  if (x[i] == 0)
 { 
return i;
 } 
}
 return -1; 
}
// test: x=[0, 1, 0] 
// Expected = 2

回答：

1.要求返回最后一个零的位置，代码返回第一个零的位置

2.x = NULL;

3.x = [1,0];

4.x = [0,1];