CC150 Arrays and Strings 1.4 ~ 1.6 Replace Spaces, String Compression, Rotate Image
1.4
题目如下：
Write a method to replace all spaces in a string with ‘%20’.
解答如下：
/**
* @author feliciafay
* @note replace space with Percentage Symbol
* @tips 1. manipulate a string from the end, extra buffer will save
* us trouble from worrying about overwriting
* 2. strings are IMMUTABLE, char arrays are not.
*
*/
public class ReplaceSpaceWithPercentageSymbol {
/*
* @str: the input string, including the white spaces and the extra space to hold %20.
* @trueLength: the length of the string, including the white spaces.
*/
String replaceSpacewithPercentageSymbol (char[] str, int trueLength) {
if (trueLength < 1) {
return "";
}
int countZero = 0;
for (int i = 0; i < trueLength; ++i) {
if (str[i] == ' ') {
++countZero;
}
}
int newLength = trueLength + countZero * 2;
str[newLength] = '\0'; //设置拷贝新字符串后的间隔符号。
newLength--;
for (int i = trueLength - 1; i >=0; --i) {
if (str[i] == ' ') {
str[newLength] = '0';
str[newLength-1] = '2';
str[newLength-2] = '%';
newLength -=3;
} else {
str[newLength--] = str[i];
//--newLength;
}
}
String result = new String(str);
return result;
}
public static void main(String[] args) {
// TODO Auto-generated method stub
ReplaceSpaceWithPercentageSymbol replacesymbol = new ReplaceSpaceWithPercentageSymbol();
char[] chararray = new char[100];
char[] chararray2 = new char[] {'a',' ',' ','b',' ',' ',' '};
System.arraycopy(chararray2, 0, chararray, 0, chararray2.length);
System.out.println(replacesymbol.replaceSpacewithPercentageSymbol(chararray, 7));
}
}
1.5
题目如下：
implement a method to perform basic string compression using the counts of repeated characters. For example, the string "aabccccaaa" would become a2b1c5a3.
解答如下：
public class BasicStringCompression {
String basicStringCompression(String input) {
String result = new String();
if (input.length() < 1) return result;
char current = input.charAt(0);
int count = 1;
StringBuilder sb = new StringBuilder();
for (int i = 1; i < input.length(); ++i) {
if (input.charAt(i) == current) {
++count;
} else {
sb.append(current);
sb.append(count);
current = input.charAt(i);
count = 1;
}
}
sb.append(current);
sb.append(count);
if (sb.length() < input.length())
return sb.toString();
else
return input;
}
public static void main(String[] args) {
// TODO Auto-generated method stub
String input = "aaaabbcdddd";
BasicStringCompression bsc = new BasicStringCompression();
System.out.println(bsc.basicStringCompression(input));
}
}
1.6
题目如下：
Given N*N matrix, rotate it by 90 degree clockwise without extra memory.
解答如下：
//implement the swap index by index.
public class RotateImage90Degree {
public void Rotate90Degree(int[][] matrix, int degree) {
for (int layer = 0; layer < degree/2; ++layer) {
int first = layer;
int last = degree - layer - 1;
int tmp = 0;
int offset = 0;
for (int i = first; i <last; ++i) { // should be very clear: "<" instead of <=
offset = i - first;
//top
tmp = matrix[first][i];
//top <- left
matrix[first][i] = matrix[last - offset][first];
//left <- bottom
matrix[last - offset][first] = matrix[last][last - offset];
//bottom <- right
matrix[last][last - offset] = matrix[i][last];
// right <- top;
matrix[i][last] = tmp;
}
}
return;
}
public void print_matrix(int[][] matrix, int degrees){
for (int i = 0; i < degrees; ++i) {
for (int j = 0; j < degrees; ++j) {
System.out.print(matrix[i][j] + " ");
}
System.out.println("");
}
}
public static void main(String[] args) {
// TODO Auto-generated method stub
int [][] my_matrix = {{1,2,3},{4,5,6},{7,8,9}};
int degree = 3;
RotateImage90Degree ri9d = new RotateImage90Degree();
ri9d.print_matrix(my_matrix, degree);
ri9d.Rotate90Degree(my_matrix, 3);
ri9d.print_matrix(my_matrix, degree);
}
}