Printing reverse of any String without using any predefined function?
How to print the reverse of the String开发者_如何学JAVA java is object orientated language without using any predefined function like reverse()?
This is the simplest solution:
System.out.print("egaugnal detatneiro tcejbo si avaj");
You can do it either recursively or iteratively (looping).
Iteratively:
static String reverseMe(String s) {
StringBuilder sb = new StringBuilder();
for(int i = s.length() - 1; i >= 0; --i)
sb.append(s.charAt(i));
return sb.toString();
}
Recursively:
static String reverseMe(String s) {
if(s.length() == 0)
return "";
return s.charAt(s.length() - 1) + reverseMe(s.substring(0,s.length()-1));
}
Well, printing itself would suggest a predefined function...
Presumably, though, you could obtain the characters and concatenate them manually in reverse (i.e. loop over it backwards). Of course, you could say concatenation is a predefined function... so maybe the char array itself. But again... why?
Is the source allowed to contain "egaugnal detatneiro tcejbo si avaj" ;-p
Also - note that string reversal is actually pretty complex if you consider unicode combining characters, surrogate pairs, etc. You should note the caveat that most string reversal mechanisms will only deal with the more common cases, but may struggle with i18n.
String reverse(String s) {
int legnth = s.length();
char[] arrayCh = s.toCharArray();
for(int i=0; i< length/2; i++) {
char ch = s.charAt(i);
arrayCh[i] = arrayCh[legnth-1-i];
arrayCh[legnth-1-i] = ch;
}
return new String(arrayCh);
}
How about a simple traverse from the end of the string to the beg:
void printRev(String str) {
for(int i=str.length()-1;i>=0;i--)
System.out.print(str.charAt(i));
}
public class StringReverse {
public static void main(String[] args) {
String s= (args[0]);
for (int i =s.length()-1; i >= 0; i--) {
System.out.print(s.charAt(i));
}
}
}
Prints the reversed string of the input.
String a="Siva";
for(int i=0;i<=a.length()-1;i++){
System.out.print(a.charAt(i));
}
for(int i = a.length() - 1; i >= 0; --i){
System.out.println(a.charAt(i));
}
First of all: Why reinvent the wheel?
That being said: Loop from the length of the string to 0 and concatenate into another string.
Here's a recursive solution that just prints the string in reverse order. It should be educational if you're trying to learn recursion. I've also made it "wrong" by actually having 2 print statements; one of them should be commented out. Try to figure out which mentally, or just run experiments. Either way, learn from it.
static void printReverse(String s) {
if (!s.isEmpty()) {
System.out.print(s.substring(0, 1));
printReverse(s.substring(1));
System.out.print(s.substring(0, 1));
}
}
Bonus points if you answer these questions:
- What is its stack requirement? Is it prone to stack overflow?
- Is it a tail recursion?
final String s = "123456789";
final char[] word = s.toCharArray();
final int l = s.length() - 2;
final int ll = s.length() - 1;
for (int i = 0; i < l; i++) {
char x = word[i];
word[i] = word[ll - i];
word[ll - i] = x;
}
System.out.println(s);
System.out.println(new String(word));
You can do it either recursively or iteratively (looping).
Iteratively:
static String reverseMe(String s) {
StringBuilder sb = new StringBuilder();
for (int i = s.length() - 1; i >= 0; --i)
sb.append(s.charAt(i));
return sb.toString();
}
Recursively:
static String reverseMe(String s) {
if (s.length() == 0)
return "";
return s.charAt(s.length() - 1) + reverseMe(s.substring(1));
}
Integer i = new Integer(15);
test(i);
System.out.println(i);
test(i);
System.out.println(i);
public static void test (Integer i) {
i = (Integer)i + 10;
}
public class StringReverse {
public static void main(String ar[]){
System.out.println(reverseMe("SRINIVAS"));
}
static String reverseMe(String s){
StringBuffer sb=new StringBuffer();
for(int i=s.length()-1;i>=0;--i){
sb.append(s.charAt(i));
}
return sb.toString();
}
}
private void rev() {
String st="hello";
String b="";
for(int i=st.length()-1;i>=0;i--){
b=b+st.charAt(i);
}
System.out.println("reverse:::"+b);
}
Try this:
public class Test {
public static void main(String[] args) {
String s = "welcome";
for( int i=0, j = (s.length())-1; i <= j; j-- ) {
char c=s.charAt(j);
System.out.print(c);
}
}
}
What is suprising is that most of the answers are wrong! When Unicode is used. Seems like no one understands that java uses UTF-16 under the hood for Text encoding.
Here is my simple answer.
static String reverseMe(String s) {
StringBuilder sb = new StringBuilder();
int count = s.codePointCount(0,s.length());
for(int i = count - 1; i >= 0; --i)
sb.append(Character.toChars(s.codePointAt(i)));
return sb.toString();
}
this is the best solution for this
public class String_rev {
public static void main(String[] args) {
String str="Karan Rajput";
int ln=str.length();
for (int i = ln; i > 0; i--) {
System.out.print(str.charAt(i-1));
}
}
}
public class ReverseString {
public static void main(String [] args) {
String s = "reverse string" ;
String b = "";
for (int i = 0; i < s.length(); i++ ){
b= b + s.substring(s.length()-1-i, s.length()-i);
}
System.out.println(b);
}
public static void main(String[] args) {
String str = "hello world here I am";
StringTokenizer strToken = new StringTokenizer(str);
int token = strToken.countTokens();
String str1 [] = new String[token];
char chr[] = new char[str.length()];
int counter = 0;
for(int j=0; j < str.length(); j++) {
if(str.charAt(j) != ' ') {
chr[j] = str.charAt(j);
}else {
str1[counter++] = new String(chr).trim();
chr = new char[str.length()];
}
}
str1[counter++] = new String(chr).trim();
for(int i=str1.length-1; i >= 0 ; i--) {
System.out.println(str1[i]);
}
}
O/P is: am I here world hello
I had this a while back, and having answered with the obvious StringBuffer.reverse() answer, they then asked 'Can you reverse a char array without using those API methods and achieve the result without spooling into a new char array?'
At the time I recognised that I only needed to iterate over half the length of the char array, but made a bit of a hash of explaining the actual code that needed to go into it (it was a verbal question). Anyway, I tried it when I got home and came up with this:
public class StringReverse {
public static void main(String[] args){
String a = "String";
char[] aChar = a.toCharArray();
for (int i = (aChar.length-1)/2 ; i >= 0 ; i--){
int posA = i;
int posB = (aChar.length-1-i);
char tmpA = aChar[posA];
char tmpB = aChar[posB];
System.out.println("Setting " + posA + " to " + tmpB);
System.out.println("Setting " + posB + " to " + tmpA);
aChar[posA] = tmpB;
aChar[posB] = tmpA;
}
System.out.println(aChar);
}
}
You can obviously achieve this with less code, but I think the temporary assignments in the method make it more clear what the code is doing.
Outputs something like:
Setting 2 to i
Setting 3 to r
Setting 1 to n
Setting 4 to t
Setting 0 to g
Setting 5 to S
gnirtS
More of an interview question than a homework question, I'd say.
public String reverse(String arg)
{
String tmp = null;
if (arg.length() == 1)
{
return arg;
}
else
{
String lastChar = arg.substring(arg.length()-1,arg.length());
String remainingString = arg.substring(0, arg.length() -1);
tmp = lastChar + reverse(remainingString);
return tmp;
}
}
import java.util.*;
public class Restring {
public static void main(String[] args) {
String input,output;
Scanner kbd=new Scanner(System.in);
System.out.println("Please Enter a String");
input=kbd.nextLine();
int n=input.length();
char tmp[]=new char[n];
char nxt[]=new char[n];
tmp=input.toCharArray();
int m=0;
for(int i=n-1;i>=0;i--)
{
nxt[m]=tmp[i];
m++;
}
System.out.print("Reversed String is ");
for(int i=0;i<n;i++)
{
System.out.print(nxt[i]);
}
}
public class ReverseWithoutStringAPI {
public static void main(String[] args) {
String st="hello";
StringBuffer b=new StringBuffer();
for(int i=st.length()-1;i>=0;i--){
b.append(st.charAt(i)); }
System.out.println("reverse:::"+b);
}
}
String x = "stack overflow";
String reversed = "";
for(int i = x.length()-1 ; i>=0; i--){
reversed = reversed+ x.charAt(i);
}
System.out.println("reversed string is : "+ reversed);
Here you go:
public static void main (String[] args) {
System.out.println(reverserString("Akshay"));
}
private static String reverserString(String src) {
char[] sArr = src.toCharArray();
char[] dArr = new char[sArr.length];
for(int i=sArr.length; i>0; i--) {
dArr[sArr.length-i] = sArr[i-1];
}
return new String(dArr);
}
public class MyStack {
private int maxSize;
private char[] stackArray;
private int top;
public MyStack(int s) {
maxSize = s;
stackArray = new char[maxSize];
top = -1;
}
public void push(char j) {
stackArray[++top] = j;
}
public char pop() {
return stackArray[top--];
}
public char peek() {
return stackArray[top];
}
public boolean isEmpty() {
return (top == -1);
}
public boolean isFull() {
return (top == maxSize - 1);
}
public static void main(String[] args) {
MyStack theStack = new MyStack(10);
String s="abcd";
for(int i=0;i<s.length();i++)
theStack.push(s.charAt(i));
for(int i=0;i<s.length();i++)
System.out.println(theStack.pop());
}
public class ReverseString {
public static void main(String[] args) {
reverseString("HELLO");
}
public static String reverseString(String s){
char []arr=s.toCharArray();
for(int i= (arr.length)-1;i>=0;i--){
System.out.print(arr[i]);
}
String str=String.copyValueOf(arr);
return str;
}
package com.ofs;
public class ReverseWordsInString{
public static void main(String[] args) {
String str = "welcome to the new world and how are you feeling ?";
// Get the Java runtime
Runtime runtime = Runtime.getRuntime();
// Run the garbage collector
runtime.gc();
// Calculate the used memory
long firstUsageMemory = runtime.totalMemory() - runtime.freeMemory();
System.out.println("Used memory in bytes: " + firstUsageMemory);
System.out.println(str);
str = new StringBuffer(str).reverse().toString();
int count = 0;
int preValue = 0;
int lastspaceIndexVal = str.lastIndexOf(" ");
int strLen = str.length();
for (int i = 0; i < strLen - 1; i++) {
if (Character.isWhitespace(str.charAt(i))) {
if (i - preValue == 1 && count == 0) {
str = str.substring(0, preValue) + str.charAt(i - 1)
+ str.substring(i, strLen);
preValue = i;
count++;
} else if (i - preValue == 2 && count == 0) {
str = str.substring(0, preValue) + str.charAt(i - 1)
+ str.charAt(i - 2) + str.substring(i, strLen);
preValue = i;
count++;
} else if (i - preValue == 3 && count == 0) {
str = str.substring(0, preValue) + str.charAt(i - 1)
+ str.charAt(i - 2) + str.charAt(i - 3)
+ str.substring(i, strLen);
preValue = i;
count++;
} else if (i - preValue == 4 && count == 0) {
str = str.substring(0, preValue) + str.charAt(i - 1)
+ str.charAt(i - 2) + str.charAt(i - 3)
+ str.charAt(i - 4) + str.substring(i, strLen);
preValue = i;
count++;
} else if (i - preValue == 5 && count == 0) {
str = str.substring(0, preValue) + str.charAt(i - 1)
+ str.substring(i - 2, i - 1) + str.charAt(i - 3)
+ str.charAt(i - 3) + str.charAt(i - 5)
+ str.substring(i, strLen);
preValue = i;
count++;
} else if (i - preValue == 6 && count == 0) {
str = str.substring(0, preValue) + str.charAt(i - 1)
+ str.charAt(i - 2) + str.charAt(i - 3)
+ str.charAt(i - 4) + str.charAt(i - 5)
+ str.charAt(i - 6) + str.substring(i, strLen);
preValue = i;
count++;
} else if (i - preValue == 7 && count == 0) {
str = str.substring(0, preValue) + str.charAt(i - 1)
+ str.charAt(i - 2) + str.charAt(i - 3)
+ str.charAt(i - 4) + str.charAt(i - 5)
+ str.charAt(i - 6) + str.charAt(i - 7)
+ str.substring(i, strLen);
preValue = i;
count++;
} else if (i - preValue == 8 && count == 0) {
str = str.substring(0, preValue) + str.charAt(i - 1)
+ str.charAt(i - 2) + str.charAt(i - 3)
+ str.charAt(i - 4) + str.charAt(i - 5)
+ str.charAt(i - 6) + str.charAt(i - 7)
+ str.charAt(i - 8) + str.substring(i, strLen);
preValue = i;
count++;
} else if (i - preValue == 2 && count != 0) {
str = str.substring(0, preValue) + str.charAt(i - 1)
+ str.substring(i, strLen);
preValue = i;
} else if (i - preValue == 3 && count != 0) {
str = str.substring(0, preValue + 1) + str.charAt(i - 1)
+ str.charAt(i - 2) + str.substring(i, strLen);
preValue = i;
} else if (i - preValue == 4 && count != 0) {
str = str.substring(0, preValue + 1) + str.charAt(i - 1)
+ str.charAt(i - 2) + str.charAt(i - 3)
+ str.substring(i, strLen);
preValue = i;
} else if (i - preValue == 5 && count != 0) {
str = str.substring(0, preValue + 1) + str.charAt(i - 1)
+ str.charAt(i - 2) + str.charAt(i - 3)
+ str.charAt(i - 4) + str.substring(i, strLen);
preValue = i;
count++;
} else if (i - preValue == 6 && count != 0) {
str = str.substring(0, preValue + 1) + str.charAt(i - 1)
+ str.charAt(i - 2) + str.charAt(i - 3)
+ str.charAt(i - 4) + str.charAt(i - 5)
+ str.substring(i, strLen);
preValue = i;
count++;
} else if (i - preValue == 7 && count != 0) {
str = str.substring(0, preValue + 1) + str.charAt(i - 1)
+ str.charAt(i - 2) + str.charAt(i - 3)
+ str.charAt(i - 4) + str.charAt(i - 5)
+ str.charAt(i - 6) + str.substring(i, strLen);
preValue = i;
count++;
} else if (i - preValue == 8 && count != 0) {
str = str.substring(0, preValue + 1) + str.charAt(i - 1)
+ str.charAt(i - 2) + str.charAt(i - 3)
+ str.charAt(i - 4) + str.charAt(i - 5)
+ str.charAt(i - 6) + str.charAt(i - 7)
+ str.substring(i, strLen);
preValue = i;
count++;
}
if (lastspaceIndexVal == preValue) {
if (strLen - lastspaceIndexVal == 2 && count != 0) {
str = str.substring(0, preValue + 1)
+ str.charAt(strLen - 1);
preValue = i;
} else if (strLen - lastspaceIndexVal == 3 && count != 0) {
str = str.substring(0, preValue + 1)
+ str.charAt(strLen - 1)
+ str.charAt(strLen - 2);
preValue = i;
} else if (strLen - lastspaceIndexVal == 4 && count != 0) {
str = str.substring(0, preValue + 1)
+ str.charAt(strLen - 1)
+ str.charAt(strLen - 2)
+ str.charAt(strLen - 3);
preValue = i;
count++;
} else if (strLen - lastspaceIndexVal == 5 && count != 0) {
str = str.substring(0, preValue + 1)
+ str.charAt(strLen - 1)
+ str.charAt(strLen - 2)
+ str.charAt(strLen - 3)
+ str.charAt(strLen - 4);
preValue = i;
} else if (strLen - lastspaceIndexVal == 6 && count != 0) {
str = str.substring(0, preValue + 1)
+ str.charAt(strLen - 1)
+ str.charAt(strLen - 2)
+ str.charAt(strLen - 3)
+ str.charAt(strLen - 4)
+ str.charAt(strLen - 5);
preValue = i;
count++;
} else if (strLen - lastspaceIndexVal == 7 && count != 0) {
str = str.substring(0, preValue + 1)
+ str.charAt(strLen - 1)
+ str.charAt(strLen - 2)
+ str.charAt(strLen - 3)
+ str.charAt(strLen - 4)
+ str.charAt(strLen - 5)
+ str.charAt(strLen - 6);
preValue = i;
} else if (strLen - lastspaceIndexVal == 8 && count != 0) {
str = str.substring(0, preValue + 1)
+ str.charAt(strLen - 1)
+ str.charAt(strLen - 2)
+ str.charAt(strLen - 3)
+ str.charAt(strLen - 4)
+ str.charAt(strLen - 5)
+ str.charAt(strLen - 6)
+ str.charAt(strLen - 7);
preValue = i;
}
}
}
}
runtime.gc();
// Calculate the used memory
long SecondaryUsageMemory = runtime.totalMemory()
- runtime.freeMemory();
System.out.println("Used memory in bytes: " + SecondaryUsageMemory);
System.out.println(str);
}
}
ReverseString.java
public class ReverseString {
public static void main(String[] args) {
String str = "Ranga Reddy";
String revStr = reverseStr(str);
System.out.println(revStr);
}
// Way1 - Recursive
public static String reverseStr(String str) {
char arrStr[] = reverseString(0, str.toCharArray());
return new String(arrStr);
}
private static char[] reverseString(int charIndex, char[] arr) {
if (charIndex > arr.length - (charIndex+1)) {
return arr;
}
int startIndex = charIndex;
int endIndex = arr.length - (charIndex+1);
char temp = arr[startIndex];
arr[startIndex] = arr[endIndex];
arr[endIndex] = temp;
charIndex++;
return reverseString(charIndex++, arr);
}
// Way2
private static String strReverse(String str) {
char ch[] = new char[str.length()];
for (int i = str.length() - 1, j = 0; i >= 0; i--) {
ch[j++] = str.charAt(i);
}
return new String(ch);
}
}
It is very simple using while loop
public class Test {
public static void main(String[] args) {
String name = "subha chandra";
int len = name.length();
while(len > 0){
len--;
char c = name.charAt(len);
System.out.print(c); // use String.valueOf(c) to convert char to String
}
}
}
import java.util.Scanner;
public class StringReverse {
public static void main(String[] args) {
//Read user Data From Console
Scanner sc = new Scanner(System.in);
System.out.println("Enter Your String:");
//Take an String so that it can Store the string data
String s1 = sc.nextLine();
//split the string and keep in an array
String[] s2 = s1.split(" ");
String s3 = " ";
//reverse the string and placed in an String s3
for (int i = 0; i < s2.length; i++) {
for (int j= s2[i].length()-1;j>=0;j--) {
s3 += s2[i].charAt(j);
}//for
s3 += " ";
}//for
System.out.println("After Reverse: "+s3);
}//main
}//StringReverse
It can be done this way also
char c[]=str.toCharArray();
int i=c.lenght-1;
public void printReverseString(char[] c, int i){
if(i==-1) return;
System.out.println(c[i]);
printReverseString(c,--i);
}
加载中,请稍侯......
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