Given a string, compute recursively (no loops) [closed]

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Given a string, compute recursively (no loops) the number of times lowercase "hi" appears in the string

countHi("xxhixx") -> 1

countHi("xhixhixx") -> 2

countHi("hi") -> 1

public class Tester {

    /**
     * @param args
     */
    public static void main(String[] args开发者_如何转开发) {
        // TODO Auto-generated method stub

        int count = countHi("xxhixx");


        System.out.println("countHi: " + count);


    }

    public static int countHi(String s) {
        if (s.length() == 0) {
            return 0;
        }

        int spot = s.indexOf("hi");

        if(spot > 0)
        {   
            String nextString = s.substring(spot + 2);
            return 1 + countHi(nextString);
        }
        return 1;

    }
}

---

Should work with the following code:

public static int countHi(String s) {
    return countHi(s, 0);
}

public static int countHi(String s, int pos) {
    if (s.length() - pos < 2) {
        return 0;
    }

    int result = 0;
    if(s.charAt(pos) == 'h' && s.charAt(pos + 1) == 'i') {
        result++;
    }

    return result + countHi(s, pos + 2);
}

---

  F(x[1...n]) = 
     if the string starts with "hi" then 1 + F(x[3...n])
     else F(x[2...n])

---

Your recursive function will need a parameter that tells it where in the string to start looking. If the character at that position is 'h', then check whether the one after it is 'i'; if it is, you've found a match.

For the recursive call that checks the remainder of the string, pass the index of the next character if it wasn't 'i', or two characters ahead if it was.

(I'm giving just a description instead of actual code because this looks like a homework question.)

---

package com.indivunet.utils;

import static org.junit.Assert.assertEquals;

import org.junit.Test;

public class Tester
{

    /**
     * @param args
     */
    public static void main(String[] args)
    {
        printCountFor("xxhixx", 1);
        printCountFor("", 0);
        printCountFor("xxhixxhihi", 3);
        printCountFor(null, 0);
    }

    @Test
    public void countHi()
    {
        assertAndPrint("xxhixx", 1);
        assertAndPrint("", 0);
        assertAndPrint("xxhixxhihi", 3);
        assertAndPrint(null, 0);
    }

    private void assertAndPrint(String string, int expectedCount)
    {
        int count = printCountFor(string, expectedCount);
        assertEquals(expectedCount, count);
    }

    private static int printCountFor(String string, int expected)
    {
        int count = countHi(string);
        System.out.println("string: \"" + string + "\" expected: " + expected + " count: " + count);
        return count;
    }

    public static int countHi(String s)
    {
        if (s == null)
        {
            return 0;
        }

        int count = 0;
        boolean hiSpotted = true;
        while (hiSpotted)
        {
            int startOfNextHi = s.indexOf("hi");
            hiSpotted = startOfNextHi >= 0;
            if (!hiSpotted)
            {
                return count;
            }
            s = s.substring(startOfNextHi + 2);
            count++;
        }
        return count;
    }
}

---

public static int recCountHi(String str) {        
    if(str.length() < 2) {
        return 0;
    }
    if(str.substring(0, 2).equals("hi")) {            
        return 1 + recCountHi(str.substring(1));            
    } 
    return recCountHi(str.substring(1));        
}