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CombinationSumIII.java
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CombinationSumIII.java
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package com.leetcode;
import java.util.ArrayList;
import java.util.List;
public class CombinationSumIII {
//https://leetcode.com/problems/combination-sum-iii/
/**
Example 1:
Input: k = 3, n = 7
Output: [[1,2,4]]
Explanation:
1 + 2 + 4 = 7
There are no other valid combinations.
Example 2:
Input: k = 3, n = 9
Output: [[1,2,6],[1,3,5],[2,3,4]]
Explanation:
1 + 2 + 6 = 9
1 + 3 + 5 = 9
2 + 3 + 4 = 9
There are no other valid combinations.
Example 3:
Input: k = 4, n = 1
Output: []
Explanation: There are no valid combinations.
Using 4 different numbers in the range [1,9], the smallest sum we can get is 1+2+3+4 = 10 and since 10 > 1, there are no valid combination.
**/
class Solution {
public List<List<Integer>> combinationSum3(int k, int n) {
List<Integer> nums = new ArrayList<>();
for(int i = 1 ; i <=9 ; i++){
nums.add(i);
}
List<Integer> list = new ArrayList<>();
List<List<Integer>> result = new ArrayList<>();
backtrack(0,nums,0,k,n,list,result);
return result;
}
public void backtrack(int start,List<Integer> nums, Integer sum , int k , int n ,List<Integer> list, List<List<Integer>> result){
if(list.size() == k && sum == n){
result.add(new ArrayList<>(list));
}
for(int i = start ; i < nums.size() ; i++){
list.add(nums.get(i));
sum = sum + nums.get(i);
backtrack(i+1,nums,sum,k,n,list,result);
sum = sum - nums.get(i);
list.remove(list.size()-1);
}
}
}
}