[leetcode] 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.

Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).

The solution set must not contain duplicate combinations.

For example, given candidate set10,1,2,7,6,1,5and target8,
A solution set is:
[1, 7]
[1, 2, 5]
[2, 6]

[1, 1, 6]

https://oj.leetcode.com/problems/combination-sum-ii/

import java.util.ArrayList;
import java.util.Arrays;

public class Solution {
public ArrayList<ArrayList<Integer>> combinationSum2(int[] num,
int target) {
ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
if (num == null || num.length == 0)
return result;

int n = num.length;

Arrays.sort(num);
ArrayList<Integer> list = new ArrayList<Integer>();

dfs(0, num, target, list, result);

return result;
}

private void dfs(int level, int[] a, int num, ArrayList<Integer> list,
ArrayList<ArrayList<Integer>> result) {
if (num == 0) {
result.add(new ArrayList<Integer>(list));
} else if (num < 0)
return;
else {
for (int i = level; i < a.length; i++) {
if (a[i] <= num) {
list.add(a[i]);
dfs(i + 1, a, num - a[i], list, result);
list.remove(list.size() - 1);
while (i < a.length - 1 && a[i] == a[i + 1])
i++;
}

}

}
}

public static void main(String[] args) {
System.out.println(new Solution().combinationSum2(new int[] { 10, 1, 2,
7, 6, 1, 5 }, 8));
System.out.println(new Solution().combinationSum2(new int[] { 1, 1, 1,
2, 2 }, 3));
}

}

第二遍记录：

相比上题目，只修改了一个地方，新的start=i+1，表示下个元素从后面取。

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Solution {
public List<List<Integer>> combinationSum2(int[] candidates, int target) {
List<List<Integer>> res = new ArrayList<List<Integer>>();
if (candidates == null || candidates.length == 0)
return res;
Arrays.sort(candidates);
List<Integer> tmp = new ArrayList<Integer>();
combine(candidates, res, tmp, target, 0);
return res;
}

private void combine(int[] candidates, List<List<Integer>> res, List<Integer> tmp, int target, int start) {
if (target < 0)
return;
if (target == 0) {
res.add(new ArrayList<Integer>(tmp));
return;
} else {
for (int i = start; i < candidates.length; i++) {
// 注意这步的去重
if (i == start || candidates[i] != candidates[i - 1]) {
tmp.add(candidates[i]);
// 注意新的start是i+1,表示只能从以选中元素的后面玄素开始选。
combine(candidates, res, tmp, target - candidates[i], i + 1);
tmp.remove(tmp.size() - 1);
}
}

}
}

public static void main(String[] args) {
System.out.println(new Solution().combinationSum2(new int[] { 1, 1, 1, 1, 3, 6, 7 }, 5));
System.out.println(new Solution().combinationSum2(new int[] { 10, 1, 2, 7, 6, 1, 5 }, 8));
}

}

参考：

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