我正在尝试为作业编写程序。要求是递归创建Pascal的Triangle，然后打印给定的行。但是，在编译程序后，我得到了几个ArrayIndexOutOfBoundsExceptions。这是堆栈跟踪：java.lang.ArrayIndexOutOfBoundsException: 10 at pasTriangle.populateT(pasTriangle.java:79) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:93) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java: 93) at pasTriangle.populateT(pasTriangle.java:86) at pasTriangle.populateT(pasTriangle.java:86)at pasTriangle.populateT(pasTriangle.java:86)at pasTriangle.populateT(pasTriangle.java:86)at pasTriangle.populateT(pasTriangle.java:86)
有人知道我在做什么错吗？我已经尝试了所有方法，尤其是改变调味品，但没有任何效果。这是我的代码：
public class pasTriangle
{
private int size, row, col; //Represents the number of lines the triangle has.
private int [][] pTriangle; //2-D array to hold int values of triangle
/* ****************************************************************************************************************************************************
Constructor creates a 2D array to hold the Pascales triangle. Note the number of numbers on each line is the same as the number of lines in
the triangle, so size can be used for both values. Calls populateT method to populate the triangle.
***************************************************************************************************************************************************/
public pasTriangle(int size)
{
this.size = size;
pTriangle = new int[size][size];
}
/* ****************************************************************************************************************************************************
Method which populates the Pascal's Triangle recursively. Note case where size = 1, recursion does not occur since only 1 integer can be added
to array.
Also note base case where base of triangle is reached and recursion stops.
Also note cases for first and last value of each line (row).
Appropriate values added to each index according to conditions.
*********************************************************************************************************************************************************/
public void populateT(int row, int col)
{
if(size > 0 && size == 1 && row < size)
{
pTriangle[0][0] = 1;
}
else if(size > 1 && row < size)
{
if (col==0 && row == 0) //First value.
{
pTriangle[row][col] = 1;
}
else if (row != 0 && col == 0 || col == pTriangle[row].length-1)
{
pTriangle [row][col] = 1; //1 Set for first value in each line and last value in each line.
}
else if(row > 1 && col != 0 && col != pTriangle[row].length-1) //Values in between first and last calculated from the two above them, to left and right.
{
pTriangle[row][col] = (pTriangle[row-1][col-1]) + (pTriangle[row-1][col+1]);
//Line 79, exception here.
}
if (col < pTriangle[row].length && row < pTriangle.length) //Move over and give values to indexes recursively until end of row is reached
{ **//Line 87, exception here.**
populateT(row, col+1);
}
else if (col >= pTriangle[row].length && row < pTriangle.length) //If end of row is reached and number of rows is not exceeded.
{
col = 0; //Col reset.
**//Line 93 Exception here.**
populateT(row+1, col);
}
}
}
/* ***********************************************************************************************************************************************
Prints a string containing the values on a given line of the pasTriangle. Note 1 is subtracted from lineNumber to get correct index.
***********************************************************************************************************************************************/
public String getLine(int lineNumber)
{
lineNumber = lineNumber - 1;
String result = "";
for(int biz = 0; biz < pTriangle[lineNumber].length; biz++)
{
result += Integer.toString(pTriangle[lineNumber][biz]);
}
System.out.println(result+"/n");
return result;
}
}
{
public static void main (String [] args)
{
try{
pasTriangle T1 = new pasTriangle(1);
pasTriangle T2 = new pasTriangle(9);
pasTriangle T3 = new pasTriangle(3);
pasTriangle T4 = new pasTriangle(5); //Triangle with only one line created (so not a triangle); test for condition size == 1.
T1.populateT(0, 0);
T2.populateT(0, 0);
T3.populateT(0, 0);
T4.populateT(0, 0);
T1.getLine(1);
T2.getLine(4);
T2.getLine(9); //Test for last line.
T3.getLine(1); //Test for first line.
T3.getLine(2);
T4.getLine(1); //Test for first line.
}
catch(ArrayIndexOutOfBoundsException exception)
{
exception.printStackTrace();
}
}
}
最佳答案
ArrayIndexOutOfoundsException似乎即将到来，因为此行允许递归以无效的row索引继续。
else if (col >= pTriangle[row].length && row < pTriangle.length)
row变量可以是pTriangle.length - 1，然后您调用populateT(row+1, col)，将pTriangle.length传递给递归调用。然后，该递归调用最终尝试访问无效的row索引，从而导致异常。将其更改为row < pTriangle.length - 1将解决即时异常问题。直接位于其上方的条件
row < pTriangle.length控制何时移动到下一列，但是您在这里不需要它。您不是在这里修改row。另外，您将希望在匹配
row时停止列递归，而不是在匹配row的物理端时停止，因此这两个条件都需要更改。将if (col < pTriangle[row].length && row < pTriangle.length)更改为if (col < row)，将else if (col >= pTriangle[row].length && row < pTriangle.length)更改为else if (col >= row && row < pTriangle.length - 1)。在这些条件之上，需要在代码中进行类似的更改，以确定是写
1还是添加上一行的相关数字。将else if (row != 0 && col == 0 || col == pTriangle[row].length-1)更改为else if (row != 0 && col == 0 || col == row)，将else if(row > 1 && col != 0 && col != pTriangle[row].length-1)更改为else if(row > 1 && col != 0 && col != row)。当您添加上一行的元素以写入非
1值时，似乎您添加的是错误的元素。假设有效的数据结构如下所示...[1][0][0][0]
[1][1][0][0]
[1][2][1][0]
[1][3][3][1]
您需要在上方和左侧添加元素，在上方直接添加元素。将
(pTriangle[row-1][col-1]) + (pTriangle[row-1][col+1]);更改为(pTriangle[row-1][col-1]) + (pTriangle[row-1][col]);。 （col+1更改为col。）如果您在
getLine中更改输出代码以添加空格，则可以更好地验证数字。另外，println已经在参数后打印了新行，因此您无需附加换行符（用\n代替/n）。