/* Given an array of ints, is it possible to choose a group of some of the * ints, such that the group sums to the given target? This is a classic * backtracking recursion problem. Rather than looking at the whole array, * our convention is to consider the part of the array starting at index * start and continuing to the end of the array. The caller can specify the * whole array simply by passing start as 0. No loops are needed -- the * recursive calls progress down the array. */ public boolean groupSum(int start, int[] nums, int target) { if(start >= nums.length) return target == 0; if(groupSum(start+1, nums, target - nums[start])) return true; if(groupSum(start+1, nums, target)) return true; return false; }