无法使 Pascal 的三角递归程序运行 --Java
Cannot Get Pascal's Triangle Recursive Program to Work --Java
我正在尝试为作业编写程序。要求是递归地创建 Pascal 的三角形，然后打印给定的行。然而，在编译我的程序之后，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)
有谁知道我做错了什么？我已经尝试了所有方法，尤其是更改条件，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();
}
}
}
ArrayIndexOutOfoundsException 似乎即将到来，因为此行允许递归继续使用无效的 row 索引。
else if (col >= pTriangle[row].length && row < pTriangle.length)
row 变量可以是 pTriangle.length - 1，然后你调用 populateT(row+1, col)，将 pTriangle.length 传递给递归调用。然后该递归调用最终会尝试访问无效的 row 索引，从而导致异常。将其更改为 row < pTriangle.length - 1 将解决当前的异常问题。
它上面的条件，row < pTriangle.length，控制何时移动到下一列，但你在这里不需要它；您没有在此处修改 row。
此外，当您匹配 row 时，您会希望停止列递归，而不是当您匹配 row 的物理结尾时，所以 both 条件需要改变。将 if (col < pTriangle[row].length && row < pTriangle.length) 更改为 if (col < row)，并将 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，以确定是写一个 1 还是添加上面一行中的相关数字。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)。
当您添加前一行的元素以写入非 1 值时，您似乎添加了错误的元素。假设一个有效的数据结构看起来像这样...
[1][0][0][0]
[1][1][0][0]
[1][2][1][0]
[1][3][3][1]
您需要将上方和左侧的元素添加到正上方的元素。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。）
如果您更改 getLine 中的输出代码以添加 space，您将能够更好地验证您的数字。此外，println 已经在您的参数后打印了一个新行，因此您无需添加换行符（\n 而不是 /n）。
我正在尝试为作业编写程序。要求是递归地创建 Pascal 的三角形，然后打印给定的行。然而，在编译我的程序之后，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)
有谁知道我做错了什么？我已经尝试了所有方法，尤其是更改条件，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();
}
}
}
ArrayIndexOutOfoundsException 似乎即将到来，因为此行允许递归继续使用无效的 row 索引。
else if (col >= pTriangle[row].length && row < pTriangle.length)
row 变量可以是 pTriangle.length - 1，然后你调用 populateT(row+1, col)，将 pTriangle.length 传递给递归调用。然后该递归调用最终会尝试访问无效的 row 索引，从而导致异常。将其更改为 row < pTriangle.length - 1 将解决当前的异常问题。
它上面的条件，row < pTriangle.length，控制何时移动到下一列，但你在这里不需要它；您没有在此处修改 row。
此外，当您匹配 row 时，您会希望停止列递归，而不是当您匹配 row 的物理结尾时，所以 both 条件需要改变。将 if (col < pTriangle[row].length && row < pTriangle.length) 更改为 if (col < row)，并将 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，以确定是写一个 1 还是添加上面一行中的相关数字。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)。
当您添加前一行的元素以写入非 1 值时，您似乎添加了错误的元素。假设一个有效的数据结构看起来像这样...
[1][0][0][0]
[1][1][0][0]
[1][2][1][0]
[1][3][3][1]
您需要将上方和左侧的元素添加到正上方的元素。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。）
如果您更改 getLine 中的输出代码以添加 space，您将能够更好地验证您的数字。此外，println 已经在您的参数后打印了一个新行，因此您无需添加换行符（\n 而不是 /n）。