leeetcode-40. Combination Sum II
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40. Combination Sum II
Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.
Each number in C may only be used once in the combination.
Note:
- All numbers (including target) will be positive integers.
- The solution set must not contain duplicate combinations.
For example, given candidate set [10, 1, 2, 7, 6, 1, 5]
and target 8
,
A solution set is:
[ [1, 7], [1, 2, 5], [2, 6], [1, 1, 6]]
题解:
和之前的那个Combination Sum都是一脉相承的
一开始我看到问题,只是看到了元素不能重复取,所以就把前一题的递归中的 i 改成了 i + 1
但是提交完,发现还是wrong answer,原来给定的集合里的元素是可以重复的,就导致结果中的集合就会重复,所以还要加一个判定条件,当有相同的元素时,只使用最后一个元素并入递归就好:
错误的例子:
Input:[10,1,2,7,6,1,5]8
Output:[[1,1,6],[1,2,5],[1,7],[1,2,5],[1,7],[2,6]]
Expected:[[1,1,6],[1,2,5],[1,7],[2,6]]
AC的solu:
class Solution { public List<List<Integer>> combinationSum2(int[] nums, int target) { List<List<Integer>> list = new ArrayList<>(); Arrays.sort(nums); backtrack(list, new ArrayList<>(), nums, target, 0); return list; } private void backtrack(List<List<Integer>> list, List<Integer> tempList, int [] nums, int remain, int start){ if(remain < 0) return; else if(remain == 0) list.add(new ArrayList<>(tempList)); else{ for(int i = start; i < nums.length; i++){ if(i != start && nums[i] == nums[i-1]) continue; tempList.add(nums[i]); backtrack(list, tempList, nums, remain - nums[i], i+1); // not i + 1 because we can reuse same elements tempList.remove(tempList.size() - 1); } } } }
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