CodingBat: Java. Warmup-2, Part I


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The Warmup-2 section on CodingBat gently introduces string and array loops. There wasn’t much to comment since the solutions are all relatively straight-forward. All solutions were successfully tested on 13 January 2013.

stringTimes:

public String stringTimes(String str, int n) {
String result = “”;
for (int i = 0; i < n; i++) result += str; return result; } [/sourcecode] frontTimes:

public String frontTimes(String str, int n) {
String result = “”;
if (str.length() <= 3) for (int i = 0; i < n; i++) result += str; else for (int i = 0; i < n; i++) result += str.substring(0, 3); return result; } [/sourcecode] countXX:

int countXX(String str) {
int count = 0;
for (int i = 0; i < str.length() - 1; i++) if (str.substring(i, i + 2).equals("xx")) count++; return count; } [/sourcecode] doubleX:

boolean doubleX(String str) {
int firstX = str.indexOf(‘x’);
if (firstX < str.length() - 1) return str.charAt(firstX + 1) == 'x'; return false; } [/sourcecode] stringBits:

public String stringBits(String str) {
String result = “”;
for (int i = 0; i < str.length(); i++) { if (i % 2 == 0) result += str.charAt(i); } return result; } [/sourcecode] stringSplosion:

public String stringSplosion(String str) {
String result = “”;
for (int i = 0; i <= str.length(); i++) { result += str.substring(0, i); } return result; } [/sourcecode] last2:

public int last2(String str) {
int count = 0;
for (int i = 0; i < str.length() - 2; i++) { if (str.substring(i, i + 2).equals( str.substring(str.length() - 2))) count++; } return count; } [/sourcecode] arrayCount9:

public int arrayCount9(int[] nums) {
int result = 0;
for (int i = 0; i < nums.length; i++) { if (nums[i] == 9) result++; } return result; } [/sourcecode] arrayFront9:

public boolean arrayFront9(int[] nums) {
int check = (nums.length < 4) ? nums.length : 4; for (int i = 0; i < check; i++) { if (nums[i] == 9) return true; } return false; } [/sourcecode] I use the ternary operator for the sake of brevity. You can of course expand the assignment operation into an if/else block. array123:

public boolean array123(int[] nums) {
for (int i = 0; i < nums.length - 2; i++) if (nums[i] == 1 && nums[i + 1] == 2 && nums[i + 2] == 3) return true; return false; } [/sourcecode]


For further help with Coding Bat (Java), please check out my books. I am also available for tutoring.


2 thoughts on “CodingBat: Java. Warmup-2, Part I

  1. Christopher Stigson

    For string times I put:

    def string_times(str, n):
    if int(n) >= 0:
    return str * n

    And it worked. Gave me all correct. is this wrong?

    Reply

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