[英]Modifying a 2D array using a nested for loop
我正在嘗試打印出二維數組 (a) 的“中間”。 例如,對於我的代碼中給定的 arrays,我想打印:
[3,4,5,6]
[4,5,6,7]
但是我只能打印出“中間”值。 我想修改方法 inner 中的二維數組 (a)並將其打印在 main 中,而不是在嵌套的 for 循環中使用 System.out.println 。 我將如何 go 這樣做?
這是我的代碼:
public static int[][] inner(int[][] a) {
int rowL = a.length - 1;
int colL = a[1].length - 1;
for (int row = 1; row < rowL; row++) {
for (int col = 1; col < colL; col++) {
//System.out.print(a[row][col]);
a = new int[row][col];
}
System.out.println();
}
return a;
}
public static void main(String[] args) {
int[][] a = {
{1, 2, 3, 4, 5, 6},
{2, 3, 4, 5, 6, 7},
{3, 4, 5, 6, 7, 8},
{4, 5, 6, 7, 8, 9}};
for (int[] row : a) {
System.out.println(Arrays.toString(row));
}
System.out.println();
for (int[] row : inner(a)) {
System.out.println(Arrays.toString(row));
}
}
在循環外創建一個新數組,然后通過轉換兩個 arrays 之間的索引來填充循環內的數組:
public static int[][] inner (int[][] a) {
int rowL = a.length - 1;
int colL = a[1].length -1;
int[][] ret = new int[rowL - 1][colL - 1];
for (int row = 1; row < rowL; row++) {
for (int col = 1; col < colL ; col++) {
ret[row - 1][col - 1] = a[row][col];
}
}
return ret;
}
如果您只想打印中間值(我對此代碼示例的定義是: middle = full array minus first and last element ),您可以使用StringBuilder
:
public static void main(String[] args) {
int[][] a = {
{ 1, 2, 3, 4, 5, 6 },
{ 2, 3, 4, 5, 6, 7 },
{ 3, 4, 5, 6, 7, 8 },
{ 4, 5, 6, 7, 8, 9 }
};
for (int[] b : a) {
// create a String output for each inner array
StringBuilder outputBuilder = new StringBuilder();
// append an introducing bracket
outputBuilder.append("[");
// make the values to be printed ignore the first and last element
for (int i = 1; i < b.length - 1; i++) {
if (i < b.length - 2) {
/*
* append a comma plus whitespace
* if the element is not the last one to be printed
*/
outputBuilder.append(b[i]).append(", ");
} else {
// just append the last one without trailing comma plus whitespace
outputBuilder.append(b[i]);
}
}
// append a closing bracket
outputBuilder.append("]");
// print the result
System.out.println(outputBuilder.toString());
}
}
output 將是
[2, 3, 4, 5]
[3, 4, 5, 6]
[4, 5, 6, 7]
[5, 6, 7, 8]
您可以使用Arrays.stream(T[],int,int)
方法迭代數組的給定范圍:
int[][] arr = {
{1, 2, 3, 4, 5, 6},
{2, 3, 4, 5, 6, 7},
{3, 4, 5, 6, 7, 8},
{4, 5, 6, 7, 8, 9}};
int[][] middle = Arrays.stream(arr, 1, arr.length - 1)
.map(row -> Arrays.stream(row, 1, row.length - 1)
.toArray())
.toArray(int[][]::new);
// output
Arrays.stream(middle).map(Arrays::toString).forEach(System.out::println);
[3, 4, 5, 6]
[4, 5, 6, 7]
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