学校Java Week5
Week5
W5L1
Review
- Control Flow
- Condition Loops
- counter Loops
For loops
Does the exact same thing with less code
for (int i = 0; i < 10; i++)
// initial value; condition:continue to loop; change
Nested For loops
for () {
for(){
......
}
}
//print 1-100
public class Forloops_1to100 {
public static void main(String[] args) {
for (int i = 1; i<11; i++) {
for (int j = 1; j<11; j++) {
System.out.print(i*j+"\t");
}
System.out.println();
}
}
}
Arrays
After created, the size can not be changed.
An array of primitives
int [] myArray = new int[5];
int [] myArray; // Declare
myArray = new int[5]; // Get a new array object with memory for 5 ints. Assign to myArray
Array Types
String[] myArray = {"a", "b"}
boolean[] myArray = {true, false}
String[] s = new String[10]; // default values: null
boolean[] b = new boolean[4]; // default values: false
int[] i = new int[10]; // default values: 0
W5L2 ex1
public class W5L2_ex1 {
public static void main(String[] args) {
int[] nums = {1, 2, 3, 4, 5, 6};
reverseInts(nums);
printInts(nums);
}
public static void reverseInts(int[] nums) {
int t = 0;
int l = nums.length;
for (int i=0; i<l/2; i++) {
t = nums[i];
nums[i] = nums[l-i-1];
nums[l-i-1] = t;
}
}
public static void printInts(int[] nums) {
System.out.print("[");
int l = nums.length;
for (int i=0; i<l; i++) {
if (i==0) {
System.out.print(nums[i]);
} else {
System.out.print(", " + nums[i]);
}
}
System.out.print("]");
}
}
W5L2 ex2
public class W5L2_ex2 {
public static void main(String[] args) {
int [] nums = {1, 2, 3};
nums = copyEven(nums);
printInts(nums);
}
public static int[] copyEven(int[] nums) {
int l = nums.length;
int[] even = new int[(l+1)/2];
int c = 0;
for (int i=0; i<l; i++) {
if (i%2 == 0) {
even[c] = nums[i];
c++;
}
}
return even;
}
public static void printInts(int[] nums) {
System.out.print("[");
int l = nums.length;
for (int i=0; i<l; i++) {
if (i==0) {
System.out.print(nums[i]);
} else {
System.out.print(", " + nums[i]);
}
}
System.out.print("]");
}
}
W5L2 ex3
public class W5L2_ex3 {
// 两种方法均能解决
public static void main(String[] args) {
diamond(9);
diamondArray(9);
}
public static void diamond(int n) {
for (int i=1; i<n; i += 2) {
int j = (n-i)/2;
int t = j;
int k = i;
while (j>0) {
if (j == (n-i)/2) {
System.out.print(".");
} else {
System.out.print(" .");
}
j--;
}
while (k>0) {
System.out.print(" *");
k--;
}
while (t>0) {
System.out.print(" .");
t--;
}
System.out.println();
}
for (int i=n; i>=1; i -= 2) {
int j = (n-i)/2;
int t = j;
int k = i;
while (j>0) {
if (j == (n-i)/2) {
System.out.print(".");
} else {
System.out.print(" .");
}
j--;
}
while (k>0) {
if (k == n) {
System.out.print("*");
k--;
while (k>0) {
System.out.print(" *");
k--;
}
break;
}
System.out.print(" *");
k--;
}
while (t>0) {
System.out.print(" .");
t--;
}
System.out.println();
}
}
public static void diamondArray(int n) {
int[] indexArray = new int[n];
for (int i=0; i<n; i+=2) {
int t = i;
int first = (n+2-i)/2 - 1;
for (int c=0; c<=i; c++) {
indexArray[first+c] = 1;
}
for (int j=0; j<n; j++) {
if (indexArray[j] == 0) {
if (j==0) {
System.out.print(".");
} else {
System.out.print(" .");
}
} else {
if (t==n-1) {
System.out.print("*");
while (t>0) {
System.out.print(" *");
t--;
}
break;
}
System.out.print(" *");
}
}
System.out.println();
}
for (int i=n-2; i>0; i-=2) {
int left_last = (n+2-i)/2 - 2;
int right_first = (n+2+i)/2 - 1;
for (int c=0; c<=left_last; c++) {
indexArray[c] = 0;
}
for (int c=right_first; c<=n-1; c++) {
indexArray[c] = 0;
}
for (int j=0; j<n; j++) {
if (indexArray[j] == 0) {
if (j==0) {
System.out.print(".");
} else {
System.out.print(" .");
}
} else {
System.out.print(" *");
}
}
System.out.println();
}
}
}
W5L2 ex4
public class W5L2_ex4 {
public static void main(String[] args) {
printInts(arithSeries(4));
}
public static int[] arithSeries(int n) {
int[] myArray = new int[n*(n + 1)/2];
int index = 0;
for (int i=1; i<=n; i++) {
for (int j=1; j<=i; j++) {
myArray[index] = j;
index++;
}
}
return myArray;
}
public static void printInts(int[] nums) {
System.out.print("[");
int l = nums.length;
for (int i=0; i<l; i++) {
if (i==0) {
System.out.print(nums[i]);
} else {
System.out.print(", " + nums[i]);
}
}
System.out.print("]");
}
}
W5 CW1 5.1
public class W5_CW1_51 {
public static void main(String[] args) {
bandMatrix(8,0);
bandMatrix(8,1);
bandMatrix(8,2);
bandMatrix(8,3);
bandMatrix(8,4);
bandMatrix(8,5);
bandMatrix(8,6);
bandMatrix(8,7);
}
public static void bandMatrix(int n, int width) {
for (int i=0; i<n; i++) {
for (int j=0; j<n; j++) {
if (j == 0) {
int ij = i+j;
if (Math.abs(ij-2*i) <= width) {
System.out.print("*");
} else {
System.out.print(0);
}
} else {
int ij = i+j;
if (Math.abs(ij-2*i) <= width) {
System.out.print(" *");
} else {
System.out.print(" " + 0);
}
}
}
System.out.println();
}
}
}
W5 CW1 5.2
public class w5_cw1_52 {
public static void main(String[] args) {
int[] nums1 = {1, 2, 3, 4};
printInts(evenOddSwap(nums1));
int[] nums2 = {100, 25};
printInts(evenOddSwap(nums2));
int[] nums3 = {};
printInts(evenOddSwap(nums3));
int[] nums4 = {11, 55, 100, 200, 300, 7};
printInts(evenOddSwap(nums4));
}
public static int[] evenOddSwap(int[] nums) {
int l = nums.length;
boolean[] flag = new boolean[l];
int t = 0;
for (int i=0; i<l; i++) {
if (flag[i]) {
continue;
} else {
flag[i] = true;
}
if (nums[i]%2 == 0) {
for (int j=i; j<l; j++) {
if (nums[j]%2 == 1) {
t = nums[j];
nums[j] = nums[i];
nums[i] = t;
flag[j] = true;
break;
}
}
} else {
for (int j=i; j<l; j++) {
if (nums[j]%2 == 0) {
t = nums[j];
nums[j] = nums[i];
nums[i] = t;
flag[j] = true;
break;
}
}
}
}
return nums;
}
public static void printInts(int[] nums) {
System.out.print("[");
int l = nums.length;
for (int i=0; i<l; i++) {
if (i==0) {
System.out.print(nums[i]);
} else {
System.out.print(", " + nums[i]);
}
}
System.out.print("]");
}
}
