java - Looping Algorithm

Question

How do I make this:

*******
-*****-
--***--
---*---
--***--
-*****-
*******

The following is my code that I have written to try to accomplish the above, but it is not working as expected:

    public static void stars(/*int jmlBaris*/) {
    for ( int i = 7; i >= 1; i-=2) {
        for (int j = 1; j <= i; j++) {

            System.out.print("*");
        }
        System.out.println("");
    }

    for (int i = 1; i <= 7; i+=2) {
        for (int j = 1; j <= i; j++){
            System.out.print("*");
            }
        System.out.println("");
    }
}
public static void main(String[] args) {
    stars();
}
}

score 9 · Accepted Answer

This is how I might write it.

// three loops
public static void stars(int size) {
    for (int y = 0; y < size; y++) {
        for (int i = 0; i < y && i < size - y - 1; i++)
            System.out.print(' ');
        for (int i = Math.min(y, size - y - 1); i < Math.max(y + 1, size - y); i++)
            System.out.print('*');
        System.out.println();
    }
}

or

// two loops
public static void stars(int size) {
    for (int y = 0; y < size; y++) {
        for (int x = 0; x < size; x++)
            System.out.print(
                    (x >= y && x < size - y) ||
                            (x >= size - y - 1 && x <= y) ? '*' : ' ');
        System.out.println();
    }
}

or

// one loop
public static void stars(int size) {
    for (int i = 0; i < size * size; i++) {
        int y = i / size, x = i % size;
        System.out.print(
                (x >= y && x < size - y) ||
                        (x >= size - y - 1 && x <= y) ? '*' : ' ');
        if (x == size - 1)
            System.out.println();
    }
}

Note: Whether this uses one, two or three loops, the time complexity is O(N^2). A simple way to determine this is the number of stars produced is O(N^2) no matter how it is done.

score 4 · Accepted Answer

I would do something like this with substrings.

String a = "*******";  //7 stars
String blank = "        "; //7 spaces
int j = 7;
for (int i = 0; i < 7; i++) {
    if (i > j){
        System.out.print(blank.substring(0,i));
        System.out.println(a.substring(i,j));
        }
    else{
        System.out.print(blank.substring(0,j));
        System.out.println(a.substring(j,i));
        }
    j--;
}
System.out.println(a);

**Previous edit wouldn't have worked. Changes made.

This works.

score 2 · Accepted Answer

Try something like this code I compiled on IDEOne (it seems to work, though): http://ideone.com/9xZ1YB

class Main
{
    public static void main(String[] args)
    {
        stars();
    }

    static void stars()
    {
        final int MAX_WIDTH = 7;

        for (int i = 0; i < 7; ++i)
        {
            int width;

            if (i < 3) width = MAX_WIDTH - i * 2;
            else if (i > 3) width = (i - 3) * 2 + 1;
            else width = 1;

            // Before spaces

            for (int j = 0; j < (MAX_WIDTH - width) / 2; ++j)
            {
                System.out.print(" ");
            }

            // Stars

            for (int j = 0; j < width; ++j)
            {
                System.out.print("*");
            }

            // After spaces

            for (int j = 0; j < (MAX_WIDTH - width) / 2; ++j)
            {
                System.out.print(" ");
            }

            System.out.println();
        }
    }
}

score 1 · Accepted Answer

For a beginner in algorithms I would recommend you to break down the structure in sub-parts and then try to solve the pattern.

For this specific pattern it could be broken down into several triangles. Each triangle is then solved by different for loops as shown in the image below.

dividing the pattern into substructures

public static void printPattern(int num) {
    // this loop generates first 4 lines
    for (int i = 0; i < num / 2 + 1; i++) {
        // draws the red triangle of '-'
        for (int j = 0; j < i; j++) {
            System.out.print("-");
        }
        // draws the green triangle of '*'
        for (int j = i; j < num / 2 + 1; j++) {
            System.out.print("*");
        }
        // draws the blue triangle of '*'
        for (int j = i + 1; j < num / 2 + 1; j++) {
            System.out.print("*");
        }
        // draws the orange triangle of '-'
        for (int j = 0; j < i; j++) {
            System.out.print("-");
        }
        System.out.println();
    }

    /* this loop generates last 3 lines */
    for (int i = 0; i < num / 2; i++) {
        // draws the green triangle of '-'
        for (int j = i + 1; j < num / 2; j++) {
            System.out.print("-");
        }
        // draws the red triangle of '*'
        for (int j = 0; j < i + 2; j++) {
            System.out.print("*");
        }
        // draws the orange triangle of '*'
        for (int j = 0; j < i + 1; j++) {
            System.out.print("*");
        }
        // draws the blue triangle of '-'
        for (int j = i + 1; j < num / 2; j++) {
            System.out.print("-");
        }
        System.out.println();
    }
}

Using similar technique you could generate any pattern.

score 0 · Accepted Answer

If I understood you right, your problem is to print indent in lines 2-7.

Imagine same problem with asterisk symbol replaced by 'x' and whitespace replaced by '-'. Then you need to draw

xxxxxxx
-xxxxx-
--xxx--
---x---
--xxx--
-xxxxx-
xxxxxxx

That means you should output 0, 1, 2 space(s) before asterisks in first, second, thrid strings respectively. I let details for you to figure them out.

score 0 · Accepted Answer

    public static void stars(/*int jmlBaris*/){
    String starstr = "*";
    String blank = "_";
    int spaceBlank;;
    for(int i=7; i>=1;i-=2){
        spaceBlank = (7-i)*.5;
        String starrep = StringUtils.repeat(starstr, i);
        String blankrep = StrinUtils.repeat(blank, spacesBlank);
        system.out.println(blankrep + starrep + blankrep);
    }
    for(int j=3 j<=7; j+=2){
        spaceBlank = (7-j)*.5;
        starrep = StringUtils.repeat(starstr, j);
         String blankrep = StrinUtils.repeat(blank, spacesBlank);
        system.out.println(blankrep + starrep  + blankrep);
    }
}    
public static void main(String[] args){
    stars();
}

score 0 · Accepted Answer

You have little missing to put space on your code. I don't care about right space, who can see that? But left space is very important!!

Try this:

public static void stars(/*int jmlBaris*/) {
    for ( int i = 7; i >= 1; i-=2) {
        for (int k = 0; k < ((7-i) / 2); k++){ /* Missing Here */
            System.out.print(" "); /* Missing Here */
        } /* Missing Here */

        for (int j = 1; j <= i; j++) {
            System.out.print("*");
        }

        System.out.println("");
    }

    for (int i = 1; i <= 7; i+=2) {
        for (int k = 0; k < ((7-i) / 2); k++){ /* Missing Here */
            System.out.print(" "); /* Missing Here */
        } /* Missing Here */

        for (int j = 1; j <= i; j++){
            System.out.print("*");
        }

        System.out.println("");
    }
}

score 0 · Accepted Answer

    int N = 7;
    for (int y=0; y<N; y++)
    {
        for (int x=0; x<N; x++)
            System.out.print( (y-x)*(N-y-x-1)<=0 ? '*' : '-');
        System.out.println();
    }

or, more symmetrically,

    int n = 3;
    for (int y=-n; y<=n; y++)
    {
        for (int x=-n; x<=n; x++)
            System.out.print( y*y>=x*x ? '*' : '-');
        System.out.println();
    }

java - Looping Algorithm

8 回答 8

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