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CombinationSum.java
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62 lines (59 loc) · 1.9 KB
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package com.yangchd.leetcode.medium;
import java.util.ArrayList;
import java.util.List;
import java.util.Stack;
/**
* @author yangchd 2018/7/13.
*
* 39. Combination Sum
*
* Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.
* The same repeated number may be chosen from candidates unlimited number of times.
*
* Note:
* All numbers (including target) will be positive integers.
* The solution set must not contain duplicate combinations.
*
* Example 1:
* Input: candidates = [2,3,6,7], target = 7,
* A solution set is:
* [
* [7],
* [2,2,3]
* ]
*
* Example 2:
* Input: candidates = [2,3,5], target = 8,
* A solution set is:
* [
* [2,2,2,2],
* [2,3,3],
* [3,5]
* ]
*
*/
public class CombinationSum {
class Solution {
public List<List<Integer>> combinationSum(int[] candidates, int target) {
List<List<Integer>> list = new ArrayList<List<Integer>>();
Stack<Integer> numStack = new Stack<Integer>();
checkNum(candidates, target, list, numStack);
return list;
}
private void checkNum(int[] candidates, int target, List<List<Integer>> list, Stack<Integer> numStack) {
for (int i = candidates.length - 1; i >= 0; i--) {
if (candidates[i] <= target && (numStack.empty() || (!numStack.empty() && candidates[i] <= numStack.peek()))) {
numStack.push(candidates[i]);
target -= candidates[i];
if (target == 0) {
list.add(new ArrayList<Integer>(numStack));
} else {
checkNum(candidates, target, list, numStack);
}
target += candidates[i];
numStack.pop();
}
}
}
}
}