Question

所以我被要求在java中编写一个递归元音计数器，我基本上写了两个非常相似的代码，但我想知道如果我将字符串与由元音组成的字符串进行比较，我可以如何计算元音？

我的2个代码：

public static int vowels(String s) {

    if (s.length() == 0 || s == null) {
        return 0;
    } else if (s.charAt(0) == 'a' || s.charAt(0) == 'i' || s.charAt(0) == 'e' || s.charAt(0) == 'o' || s.charAt(0) == 'u') {
        return 1 + vowels(s.substring(1));
    } else {
        return vowels(s.substring(1));
    }
}

第二个：它比前一个更长但基本相同

public static int vowels(String s) {

        if(s.length() ==0){
      return 0;
       }
    } else if (s.charAt(0) == 'i') {
        return 1 + vowels(s.substring(1));
    } else if (s.charAt(0) == 'o') {
        return 1 + vowels(s.substring(1));
    } else if (s.charAt(0) == 'u') {
        return 1 + vowels(s.substring(1));
    } else if (s.charAt(0) == 'e') {
        return 1 + vowels(s.substring(1));
    } else if (s.charAt(0) == 'a') {
        return 1 + vowels(s.substring(1));
    } else {
        return 0 + vowels(s.substring(1));
    }
}

Answer 1

您可以将s.charAt(0) == 'a' || s.charAt(0) == 'i' || ...更改为"iouea".contains(Character.toString(s.charAt(0))) - 这似乎是您问题的答案但是因为你应该假设输入字符串s也包含大写元音（'A'），你应该在方法开头用s小写s = s.toLowerCase()。这样您就可以使代码更简单 UPD：出错了。已将代码更改为Character.toString

Answer 2

在字符串上调用indexOf会告诉传入的char是否在该字符串中：

if ("aeiou".indexOf(Character.toLowerCase(s.charAt(0))) != -1) {
    // first char of s is a vowel
}

Answer 3

你的意思是：

public int countVowels(String s) {
    int vowels = 0;
    s=s.toLowerCase();
    for(char c : s.toCharArray()) {
        switch(c) {
        case 'a': vowels++; break;
        case 'e': vowels++; break;
        case 'o': vowels++; break;
        case 'u': vowels++; break;
        case 'i': vowels++; break;
        case 'y': vowels++; break;
        default: 
        }
    }
    return vowels;
}

???我不会说英语很好，我使用了Translate Google

编辑：第二种方法和更短的方法：

public static int countVowels(String s) {
    int vowels = 0;
    s=s.toLowerCase();
    for(char c : s.toCharArray()) {
        if("euioa".contains(c+""))vowels++;
    }
    return vowels;
}

第二次编辑：如果你的字符串有超过10000的字符并使用递归，你有一个例外，例如：

Exception in thread "main" java.lang.StackOverflowError
at sun.nio.cs.SingleByte.withResult(Unknown Source)
at sun.nio.cs.SingleByte.access$000(Unknown Source)
at sun.nio.cs.SingleByte$Encoder.encodeArrayLoop(Unknown Source)
at sun.nio.cs.SingleByte$Encoder.encodeLoop(Unknown Source)
at java.nio.charset.CharsetEncoder.encode(Unknown Source)
at sun.nio.cs.StreamEncoder.implWrite(Unknown Source)
at sun.nio.cs.StreamEncoder.write(Unknown Source)
at java.io.OutputStreamWriter.write(Unknown Source)
at java.io.BufferedWriter.flushBuffer(Unknown Source)
at java.io.PrintStream.write(Unknown Source)
at java.io.PrintStream.print(Unknown Source)
at java.io.PrintStream.println(Unknown Source)
at Test2.main(Test2.java:24)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
at Test2.main(Test2.java:25)
    ... very very long

下一个编辑：我测试了速度计数字符：

[Test #1] Result with recursive: 4.263765 ms
[Test #1] Result without (using contains, faster method): 2.69513 ms
[Test #1] Result without (using switch): 0.346898 ms
[Test #1] Result without (using if): 0.423256 ms
[Test #1] Result without (using indexOf): 0.644943 ms

[Test #2] Result with recursive: 6.40468 ms
[Test #2] Result without (using contains, faster method): 4.177144 ms
[Test #2] Result without (using switch): 0.263149 ms
[Test #2] Result without (using if): 0.281624 ms
[Test #2] Result without (using indexOf): 0.453225 ms

[Test #3] Result with recursive: 4.314261 ms
[Test #3] Result without (using contains, faster method): 2.073998 ms
[Test #3] Result without (using switch): 0.428183 ms
[Test #3] Result without (using if): 0.36373 ms
[Test #3] Result without (using indexOf): 0.392467 ms

[Test #4] Result with recursive: 5.740032 ms
[Test #4] Result without (using contains, faster method): 2.053882 ms
[Test #4] Result without (using switch): 0.160107 ms
[Test #4] Result without (using if): 0.171192 ms
[Test #4] Result without (using indexOf): 0.230718 ms

[Test #5] Result with recursive: 3.19105 ms
[Test #5] Result without (using contains, faster method): 1.833838 ms
[Test #5] Result without (using switch): 0.144096 ms
[Test #5] Result without (using if): 0.16257 ms
[Test #5] Result without (using indexOf): 0.210192 ms

[Test #6] Result with recursive: 2.586339 ms
[Test #6] Result without (using contains, faster method): 1.41715 ms
[Test #6] Result without (using switch): 0.152718 ms
[Test #6] Result without (using if): 0.161338 ms
[Test #6] Result without (using indexOf): 0.220865 ms

[Test #7] Result with recursive: 2.445117 ms
[Test #7] Result without (using contains, faster method): 1.134295 ms
[Test #7] Result without (using switch): 0.164212 ms
[Test #7] Result without (using if): 0.083749 ms
[Test #7] Result without (using indexOf): 0.133833 ms

[Test #8] Result with recursive: 1.995997 ms
[Test #8] Result without (using contains, faster method): 0.987325 ms
[Test #8] Result without (using switch): 0.058295 ms
[Test #8] Result without (using if): 0.084569 ms
[Test #8] Result without (using indexOf): 0.130959 ms

[Test #9] Result with recursive: 4.914866 ms
[Test #9] Result without (using contains, faster method): 0.335403 ms
[Test #9] Result without (using switch): 0.057063 ms
[Test #9] Result without (using if): 0.085801 ms
[Test #9] Result without (using indexOf): 0.142865 ms

[Test #10] Result with recursive: 1.164673 ms
[Test #10] Result without (using contains, faster method): 0.330477 ms
[Test #10] Result without (using switch): 0.058295 ms
[Test #10] Result without (using if): 0.180223 ms
[Test #10] Result without (using indexOf): 0.129728 ms

[Test #11] Result with recursive: 1.089547 ms
[Test #11] Result without (using contains, faster method): 0.391646 ms
[Test #11] Result without (using switch): 0.073074 ms
[Test #11] Result without (using if): 0.307487 ms
[Test #11] Result without (using indexOf): 0.123159 ms

[Test #12] Result with recursive: 3.442706 ms
[Test #12] Result without (using contains, faster method): 0.24755 ms
[Test #12] Result without (using switch): 0.052548 ms
[Test #12] Result without (using if): 0.204855 ms
[Test #12] Result without (using indexOf): 0.123159 ms

[Test #13] Result with recursive: 0.521373 ms
[Test #13] Result without (using contains, faster method): 0.251655 ms
[Test #13] Result without (using switch): 0.047211 ms
[Test #13] Result without (using if): 0.073074 ms
[Test #13] Result without (using indexOf): 0.115359 ms

[Test #14] Result with recursive: 0.540258 ms
[Test #14] Result without (using contains, faster method): 0.261508 ms
[Test #14] Result without (using switch): 0.053779 ms
[Test #14] Result without (using if): 0.0858 ms
[Test #14] Result without (using indexOf): 0.083748 ms

[Test #15] Result with recursive: 0.554626 ms
[Test #15] Result without (using contains, faster method): 0.26315 ms
[Test #15] Result without (using switch): 0.056653 ms
[Test #15] Result without (using if): 0.078411 ms
[Test #15] Result without (using indexOf): 0.079232 ms

[Test #16] Result with recursive: 0.529994 ms
[Test #16] Result without (using contains, faster method): 0.253298 ms
[Test #16] Result without (using switch): 0.058706 ms
[Test #16] Result without (using if): 0.086622 ms
[Test #16] Result without (using indexOf): 0.087443 ms

[Test #17] Result with recursive: 0.520552 ms
[Test #17] Result without (using contains, faster method): 0.267255 ms
[Test #17] Result without (using switch): 0.055832 ms
[Test #17] Result without (using if): 0.086622 ms
[Test #17] Result without (using indexOf): 0.084569 ms

[Test #18] Result with recursive: 0.531636 ms
[Test #18] Result without (using contains, faster method): 0.260687 ms
[Test #18] Result without (using switch): 0.058706 ms
[Test #18] Result without (using if): 0.082927 ms
[Test #18] Result without (using indexOf): 0.088675 ms

[Test #19] Result with recursive: 0.654385 ms
[Test #19] Result without (using contains, faster method): 0.25494 ms
[Test #19] Result without (using switch): 0.059117 ms
[Test #19] Result without (using if): 0.090317 ms
[Test #19] Result without (using indexOf): 0.084159 ms

[Test #20] Result with recursive: 0.551342 ms
[Test #20] Result without (using contains, faster method): 0.28655 ms
[Test #20] Result without (using switch): 0.083748 ms
[Test #20] Result without (using if): 0.111664 ms
[Test #20] Result without (using indexOf): 0.081696 ms

[Test #21] Result with recursive: 1.042336 ms
[Test #21] Result without (using contains, faster method): 1.165084 ms
[Test #21] Result without (using switch): 0.068969 ms
[Test #21] Result without (using if): 0.095653 ms
[Test #21] Result without (using indexOf): 0.089496 ms

[Test #22] Result with recursive: 0.555447 ms
[Test #22] Result without (using contains, faster method): 0.27054 ms
[Test #22] Result without (using switch): 0.066095 ms
[Test #22] Result without (using if): 0.091137 ms
[Test #22] Result without (using indexOf): 0.329656 ms

[Test #23] Result with recursive: 2.345769 ms
[Test #23] Result without (using contains, faster method): 0.109611 ms
[Test #23] Result without (using switch): 0.082106 ms
[Test #23] Result without (using if): 0.09278 ms
[Test #23] Result without (using indexOf): 0.094833 ms

[Test #24] Result with recursive: 0.565711 ms
[Test #24] Result without (using contains, faster method): 0.079643 ms
[Test #24] Result without (using switch): 0.089906 ms
[Test #24] Result without (using if): 0.082517 ms
[Test #24] Result without (using indexOf): 0.088264 ms

[Test #25] Result with recursive: 0.552573 ms
[Test #25] Result without (using contains, faster method): 0.078001 ms
[Test #25] Result without (using switch): 0.052137 ms
[Test #25] Result without (using if): 0.095654 ms
[Test #25] Result without (using indexOf): 0.089085 ms

测试代码：

static int i = 0;
private static long start;
private static long end;
public static void main(String[] args) {
    for(int j=0; j<25; j++) {
        test();
    }
}
public static void test()  {
    i++;
    String string = "aurwgn iowthpbomaj yo4jpb 4y9 b0q thaioe vau  hewoimjnyoj ioajr "
            + "itwejb iwojaoehmtuwehtoawegtoam yierjspyomrahvuir auyheroiamvyirhapivthe "
            + "awibthnapeutmbhuewath huaheovgayeutn jeryhaipmvhtuwea htpaw thwuaurwgn iowthpbomaj yo4jpb 4y9 b0q thaioe vau  hewoimjnyoj ioajr "
            + "itwejb iwojaoehmtuwehtoawegtoam yierjspyomrahvuir auyheroiamvyirhapivthe "
            + "awibthnapeutmbhuewath huaheovgayeutn jeryhaipmvhtuwea htpaw thwuaurwgn iowthpbomaj yo4jpb 4y9 b0q thaioe vau  hewoimjnyoj ioajr "
            + "itwejb iwojaoehmtuwehtoawegtoam yierjspyomrahvuir auyheroiamvyirhapivthe "
            + "awibthnapeutmbhuewath huaheovgayeutn jeryhaipmvhtuwea htpaw thwuaurwgn iowthpbomaj yo4jpb 4y9 b0q thaioe vau  hewoimjnyoj ioajr "
            + "itwejb iwojaoehmtuwehtoawegtoam yierjspyomrahvuir auyheroiamvyirhapivthe "
            + "awibthnapeutmbhuewath huaheovgayeutn jeryhaipmvhtuwea htpaw thwuaurwgn iowthpbomaj yo4jpb 4y9 b0q thaioe vau  hewoimjnyoj ioajr "
            + "itwejb iwojaoehmtuwehtoawegtoam yierjspyomrahvuir auyheroiamvyirhapivthe "
            + "awibthnapeutmbhuewath huaheovgayeutn jeryhaipmvhtuwea htpaw thwu";
    start = System.nanoTime();
    countVowels2(string);
    end = System.nanoTime();
    System.out.println("[Test #"+i+"] Result with recursive: "+(end-start)/1000000.0+" ms");
    start = System.nanoTime();
    countVowels(string);
    end = System.nanoTime();
    System.out.println("[Test #"+i+"] Result without (using contains, faster method): "+(end-start)/1000000.0+" ms");
    start = System.nanoTime();
    countVowels3(string);
    end = System.nanoTime();
    System.out.println("[Test #"+i+"] Result without (using switch): "+(end-start)/1000000.0+" ms");
    start = System.nanoTime();
    countVowels4(string);
    end = System.nanoTime();
    System.out.println("[Test #"+i+"] Result without (using if): "+(end-start)/1000000.0+" ms");
    start = System.nanoTime();
    countVowels5(string);
    end = System.nanoTime();
    System.out.println("[Test #"+i+"] Result without (using indexOf): "+(end-start)/1000000.0+" ms");
    System.out.println();
}
public static int countVowels(String s) {
    int vowels = 0;
    s=s.toLowerCase();
    for(char c : s.toCharArray()) {
        if("euioa".contains(c+""))vowels++;
    }
    return vowels;
}
public static int countVowels2(String s) {
    if(s.length()==0)return 0;
    if("euioa".contains(s.charAt(0)+""))return 1+countVowels2(s.substring(1));
    return countVowels2(s.substring(1));
}
public static int countVowels3(String s) {
    int vowels = 0;
    s=s.toLowerCase();
    for(char c : s.toCharArray()) {
        switch(c) {
        case 'a': vowels++; break;
        case 'e': vowels++; break;
        case 'o': vowels++; break;
        case 'u': vowels++; break;
        case 'i': vowels++; break;
        case 'y': vowels++; break;
        default: 
        }
    }
    return vowels;
}
public static int countVowels4(String s) {
    int vowels = 0;
    s=s.toLowerCase();
    for(char c : s.toCharArray()) {
        if(c=='a'||c=='e'||c=='o'||c=='u'||c=='i'||c=='y')vowels++;
    }
    return vowels;
}
public static int countVowels5(String s) {
    int vowels = 0;
    s=s.toLowerCase();
    for(char c : s.toCharArray()) {
        if("euioa".indexOf(c)!=-1)vowels++;
    }
    return vowels;
}

递归元音计数器

3 个答案: