这道题的关键,是如何保证list的不重复,首先排序是必需的,然后第二中办法中,这一步就是很重要了。
if (i > start && candidates[i] == candidates[i - 1])
{
continue;
}
题目:
给定一个数组 candidates
和一个目标数 target
,找出 candidates
中所有可以使数字和为 target
的组合。
candidates
中的每个数字在每个组合中只能使用一次。
说明:
- 所有数字(包括目标数)都是正整数。
- 解集不能包含重复的组合。
示例 1:
输入: candidates =[10,1,2,7,6,1,5]
, target =8
, 所求解集为: [ [1, 7], [1, 2, 5], [2, 6], [1, 1, 6] ]
我的比较笨的解决办法如下:
package test;
import java.util.ArrayList;
import java.util.List;
public class LC40Try1
{
public List<List<Integer>> combinationSum2(int[] candidates, int target)
{
List<List<Integer>> ret = new ArrayList<List<Integer>>();
List<Integer> list = new ArrayList<Integer>();
sort(candidates);
dpTree(candidates, target, 0, 0, list, ret);
return ret;
}
public void sort(int[] candidates){
int len=candidates.length;
for(int i=0;i<len-1;i++){
int min=candidates[i];
int t=i;
for(int j=i+1;j<len;j++){
if(candidates[j]<min){
min=candidates[j];
t=j;
}
}
candidates[t]=candidates[i];
candidates[i]=min;
}
}
public void dpTree(int[] candidates, int target,int start,int sum,List<Integer> list,List<List<Integer>> ret){
if(sum==target){
if(ret.contains(list)){
return;
}
ret.add(new ArrayList<Integer>(list));
return;
}
if(start==candidates.length){
return;
}
if(sum+candidates[start]<=target){
sum+=candidates[start];
list.add(candidates[start]);
dpTree(candidates,target,start+1,sum,list,ret);
sum-=candidates[start];
list.remove(list.size()-1);
}
dpTree(candidates,target,start+1,sum,list,ret);
}
public static void main(String[] args)
{
LC40Try1 t = new LC40Try1();
int[] candidates={2,5,2,1,2};
int target=5;
List<List<Integer>> ret = t.combinationSum2(candidates, target);
for(int i=0;i<ret.size();i++){
List<Integer> list=ret.get(i);
for(int j=0;j<list.size();j++){
System.out.print(list.get(j)+",");
}
System.out.println("");
}
}
}
比较好的解决办法如下:值得学习:
package test;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class LC40Try2
{
public List<List<Integer>> combinationSum2(int[] candidates, int target)
{
Arrays.sort(candidates);//每次自己都忘记,但我记得貌似没有自己写的快来着
List<List<Integer>> ret = new ArrayList<List<Integer>>();
List<Integer> list = new ArrayList<Integer>();
dpTree(candidates, target, 0, 0, list, ret);
return ret;
}
public void dpTree(int[] candidates, int target, int start, int sum,
List<Integer> list, List<List<Integer>> ret)
{
if (sum == target)
{
ret.add(new ArrayList<Integer>(list));
return;
}
int len = candidates.length;
for (int i = start; i < len && sum + candidates[i] <= target; i++)
{
if (i > start && candidates[i] == candidates[i - 1])
{
continue;
}
sum += candidates[i];
list.add(candidates[i]);
dpTree(candidates, target, i + 1, sum, list, ret);
sum -= candidates[i];
list.remove(list.size() - 1);
}
}
public static void main(String[] args)
{
LC40Try2 t = new LC40Try2();
int[] candidates = { 10, 1, 2, 7, 6, 1, 5 };
int target = 8;
List<List<Integer>> ret = t.combinationSum2(candidates, target);
for (int i = 0; i < ret.size(); i++)
{
List<Integer> list = ret.get(i);
for (int j = 0; j < list.size(); j++)
{
System.out.print(list.get(j) + ",");
}
System.out.println("");
}
}
}
嘿嘿