【面试系列】编写一个程序，列出1-19所有相加为20的组合

同样是联德威的一道面试题，题不难，递归一下。

public class Test02 {
static int[] array = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
14, 15, 16, 17, 18, 19 };

private static void count(int index, int value, String str, int sum) {
for (int i = index; i < array.length; i++) {
if ((value - array[i]) == 0)// 找到一个组合
{
if ((sum - array[i]) == 0) {
System.out.println("["+str + "" + array[i]+"]=20");
}
} else if ((value - array[i]) > 0)// 继续找
{
str += array[i] + ",";
sum = sum - array[i];
for (int j = i + 1; j < array.length; j++)
count(j, value - array[i], str, sum);
}
}
}

public static void main(String[] args) {
for (int i = 0; i < array.length; i++) {
count(i, 20, "", 20);
}
}
}

运行结果为：

[1,2,3,4,10]=20

[1,2,3,5,9]=20

[1,2,3,6,8]=20

[1,2,3,14]=20

[1,2,4,5,8]=20

[1,2,4,6,7]=20

[1,2,4,13]=20

[1,2,5,12]=20

[1,2,6,11]=20

[1,2,7,10]=20

[1,2,8,9]=20

[1,2,17]=20

[1,3,4,5,7]=20

[1,3,4,12]=20

[1,3,5,11]=20

[1,3,6,10]=20

[1,3,7,9]=20

[1,3,16]=20

[1,4,5,10]=20

[1,4,6,9]=20

[1,4,7,8]=20

[1,4,15]=20

[1,5,6,8]=20

[1,5,14]=20

[1,6,13]=20

[1,7,12]=20

[1,8,11]=20

[1,9,10]=20

[1,19]=20

[2,3,4,5,6]=20

[2,3,4,11]=20

[2,3,5,10]=20

[2,3,6,9]=20

[2,3,7,8]=20

[2,3,15]=20

[2,4,5,9]=20

[2,4,6,8]=20

[2,4,14]=20

[2,5,6,7]=20

[2,5,13]=20

[2,6,12]=20

[2,7,11]=20

[2,8,10]=20

[2,18]=20

[3,4,5,8]=20

[3,4,6,7]=20

[3,4,13]=20

[3,5,12]=20

[3,6,11]=20

[3,7,10]=20

[3,8,9]=20

[3,17]=20

[4,5,11]=20

[4,6,10]=20

[4,7,9]=20

[4,16]=20

[5,6,9]=20

[5,7,8]=20

[5,15]=20

[6,14]=20

[7,13]=20

[8,12]=20

[9,11]=20