Reverse and Replace a String in Linear Time

[colin.cruise]

It would be much appreciated if I could have some help with the following problem. I would like to write a Java function that has the following interface:
public String reverseAndReplace(String original, String toBeReplaced, String replacement) { .. }

This method would do two things:
1) Reverse the words in the string.
For example, given the string: "Wealth is the product of man's capacity to think." The method would transform this sentence to: "think. to capacity man's of product the is Wealth"
2) Replace a word in the String with another word.
For example:
public String reverseAndReplace("Wealth is the product of man's capacity to think.", "think", "act");
The method would return: "act. to capacity man's of product the is Wealth"

This method should run in linear time, and it cannot use not any of Java's built-in string manipulation functions nor any third-party packages (such as Apache's StringUtils and the String.replaceAll methods) in its implementation. For example, this is illegal:

public String reverseAndReplace(String original, String toBeReplaced, String replacement) {
return StringUtils.reverseDelimited(original.replaceAll(t oBeReplaced, replacement), ' ');
}

Any help would be much appreciated and thanks in advance.

[pao]

Are you allowed to use split on a string?

[colin.cruise]

No, String.split() is not allowed. But String.length,String.charAt(int index), String.toCharArray() is allowed.

[pao]

public class StringReplace {
    
    public static void main(String[] args) {
        StringReplace replace = new StringReplace();
        String newSentence = replace.reverseAndReplace("backwards be should string This", "backwards", "forwards");
        System.out.println(newSentence);
    }
    
    public String reverseAndReplace(String original, String toBeReplaced, String replacement) {
        
        String[] backwardsSplit = original.split(" ");
        StringBuffer forwards = new StringBuffer();
        
        for(int i = backwardsSplit.length; i >0; i--) {
            String word = backwardsSplit[i - 1];
            if(word.equals(toBeReplaced)) {
                forwards.append(replacement + " ");
            } else {
                forwards.append(word + " ");
            }
        }
        
        return forwards.toString();
    }
    
}

[pao]

OK ignore that ^^ let me think of another way, I presume you are allowed to use equals?

[colin.cruise]

Yes, String.equals() is allowed.