Array & ArrayList
String
LinkedList
Stack & Queue
Recursion
1. Knapsack non-repeating items. Not Bug Free
思路一：最直接的recursion.
public static boolean exist(int[] nums, int target, int index) {
if (target == 0) {
return true;
}
if (index == nums.length || target < 0) {
return false;
}
return exist(nums, target - nums[index], index++) || exist(nums, target, index++);
}