整理一下網上關於這道題和自己關於這道題的解法

方法一: 利用a+b和b+a進行比較選擇其中數值較大的組合方式

public class Solution {

    public void maxValueNum(int[] array) {
        int len = array.length;
        String maxValueStr = "";
        for(int i=0;i<len;i++) {
            for(int j=0;j<len-1-i;j++) {
                String str = ""
 
;
                        if((array[j]+str+array[j+1]).compareTo(array[j+1]+str+array[j]) > 0) {
                    swap(array, j, (j+1));
                }
            }
            maxValueStr += array[len-1-i];
        }
        System.out.println(maxValueStr);
    }

    public void swap(int[] array
 
, int a, int b) {
        int tmp = array[a];
        array[a] = array[b];
        array[b] = tmp;
    }
}

main函式:
public class Main {

    public static void main(String[] args) {
        Solution s = new Solution();
        int[] array = {195,23,56,235,7};
        s.maxValueNum(array);
    }
}

執行結果為: 75623523195
 

方法二: 利用compare函式特性來進行排序選擇

public class Solution1 {

    public void maxValueNum(int[] array) {
        int len = array.length;
        String maxValueStr = "";
        for(int i=0;i<len;i++) {
            for(int j=0;j<len-1-i;j++) {
                if(compare(array[j], array[j+1]) > 0) {
                    swap(array, j, (j+1));
                }
            }
            maxValueStr += array[len-1-i];
        }
        System.out.println(maxValueStr);
    }

    public int compare(int a, int b) {
        int count1 = 0;
        int count2 = 0;
        int middleNum1 = a;
        int middleNum2 = b;
        while(middleNum1 != 0) {
            count1++;
            middleNum1 /= 10;
        }
        while(middleNum2 != 0) {
            count2++;
            middleNum2 /= 10;
        }
        int num1 = (int) (a*Math.pow(10,count2)+b);
        int num2 = (int) (b*Math.pow(10,count1)+a);
        return num1 > num2 ? 1 : (num1 == num2 ? 0 : -1);
    }

    public void swap(int[] array, int a, int b) {
        int tmp = array[a];
        array[a] = array[b];
        array[b] = tmp;
    }
}

main函式:
public class Main {

    public static void main(String[] args) {
        Solution1 s1 = new Solution1();
        int[] array = {195,23,56,235,7};
        s1.maxValueNum(array);
    }
}

執行結果為: 75623523195

方法三: 利用貪心演算法每次求最優值

public class Solution2 {

    public void maxValueNum(int[] array) {
        int len = array.length;
        String maxValueStr = "";
        for(int i=0;i<len;i++) {
            for(int j=0;j<len-1-i;j++) {
                String str = "";
                if((array[j]+str).compareTo(array[j+1]+str) > 0) {
                    swap(array, j, (j+1));
                }
            }
            maxValueStr += array[len-1-i];
        }
        System.out.println(maxValueStr);
    }

    public void swap(int[] array, int a, int b) {
        int tmp = array[a];
        array[a] = array[b];
        array[b] = tmp;
    }
}

main函式:
public class Main {

    public static void main(String[] args) {
        Solution2 s2 = new Solution2();
        int[] array = {195,23,56,235,7};
        s2.maxValueNum(array);
    }
}

執行結果為: 75623523195