1、移动数组元素
package day3;import java.util.Arrays;public class Demo1 {public static void main(String[] args) {int[] arr = {1,2,3,4,5,6};int k = 2;int[] arr_new = f(arr,k);for (int i : arr_new) {System.out.print(i+",");}//或System.out.println();String str = Arrays.toString(arr_new);System.out.println(str);}private static int[] f(int[] arr, int k) {int n =arr.length;k = k%n;int[] new_arr = new int[n];for (int i = 0; i < arr.length; i++) {new_arr[(i+k) % n] = arr[i];}return new_arr;}
}
结果
2、二维数组求和
package day3;public class Demo3 {public static void main(String[] args) {int [][] arr= {{1,2,3},{4,5,6},{7,8,9}};int result = sum_arr(arr);System.out.println(result);}private static int sum_arr(int[][] arr) {int sum = 0;for (int[] is : arr) {for (int is2 : is) {sum+=is2;}}return sum;}
}结果
45
3、二维数组x，y轴互换，转置二维矩阵
package day3;public class Demo4 {public static void main(String[] args) {int[][] arr = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };for (int[] is : arr) {for (int is2 : is) {System.out.print(is2 + "\t");}System.out.println();}System.out.println("=======================");int[][] newArr = f(arr);for (int[] is : newArr) {for (int is2 : is) {System.out.print(is2 + "\t");}System.out.println();}}private static int[][] f(int[][] arr) {int row = arr.length;int col = arr[0].length;int[][] newArr = new int[row][col];for (int i = 0; i < newArr.length; i++) {for (int j = 0; j < newArr.length; j++) {newArr[j][i] = arr[i][j];}}return newArr;}
}
结果
4、杨辉三角
package day3;public class Demo2 {public static void main(String[] args) {// TODO Auto-generated method stub// for (int i = 0; i < 10; i++) {// for (int j = 0; j < 10; j++) {// System.out.print("外："+i+"内："+j);// }// System.out.println();// }int n = 6; int [][] arr = new int [n+1][n+1];for (int i = 1; i < arr.length; i++) {for (int j = 1; j <=i; j++) {if(i==1||i==j) {arr[i][j]=1;}else {arr[i][j]=arr[i-1][j]+arr[i-1][j-1];}}}for (int i = 1; i < arr.length; i++) {for (int j = 1; j <=i; j++) {System.out.print(arr[i][j]+",");}System.out.println();} }
}
结果
eclipse常用快捷键
alt+/ ：常用方法
ctrl+1：补全代码
5、在数组中寻找特定值
数组的每行从左到右升序排列，每列从上到下升序排列。
package day3;public class Demo5 {public static void main(String[] args) {int[][] arr = { { 1, 4, 7 }, { 2, 5, 8 }, { 3, 6, 9 } };boolean isf = f(arr,5);System.out.println(isf);}private static boolean f(int[][] arr, int num) {if(arr == null || arr[0].length == 0 || arr.length == 0) {return false;}for (int[] is : arr) {int start = 0;int end = arr.length-1;while(start<=end) {int mid =start+(end-start)/2;if(is[mid]==num) {return true;}else if(is[mid]>num) {end = mid - 1;}else {start = mid +1;}}}return false;}}
结果
true
)