LeetCode [40] Combination Sum II

method1:

• for the i-th num, choose 0 or 1, time
• since all nums are positive, the sum of the cur is monotonously increasing
• recursion terminates if Sum >= Target 
• duplicate combination occurs if
•  the i-th num == the (i-1)-th num
• the (i-1)-th num is not selected
• the i-th num is selected
• use flag "sel" to notify the next iteration whether the (i-1)-th num was selected in the previous iterations

Ref:

[1] http://yucoding.blogspot.com/2012/12/leetcode-17-combination-sum-ii.html

• dfs method