计算机算法设计与分析 第3版》 王晓东
eg. from geeksforgeeks
Given 3 numbers {1, 3, 5}, we need to tell
the total number of ways we can form a number 'N'
using the sum of the given three numbers.
(allowing repetitions and different arrangements).
Total number of ways to form 6 is : 8
1+1+1+1+1+1
1+1+1+3
1+1+3+1
1+3+1+1
3+1+1+1
3+3
1+5
5+1