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