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// @Title: 组合总和 (Combination Sum)
// @Author: 15816537946@163.com
// @Date: 2020-06-25 07:15:36
// @Runtime: 44 ms
// @Memory: 6.3 MB
import (
	"fmt"
	"sort"
)

/*
 * @lc app=leetcode.cn id=39 lang=golang
 *
 * [39] 组合总和
 *
 * https://leetcode-cn.com/problems/combination-sum/description/
 *
 * algorithms
 * Medium (66.69%)
 * Likes:    371
 * Dislikes: 0
 * Total Accepted:    34.9K
 * Total Submissions: 52.3K
 * Testcase Example:  '[2,3,6,7]\n7'
 *
 * 给定一个无重复元素的数组 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 中的数字可以无限制重复被选取。
 *
 * 说明:
 *
 *
 * 所有数字(包括 target)都是正整数。
 * 解集不能包含重复的组合。
 *
 *
 * 示例 1:
 *
 * 输入: candidates = [2,3,6,7], target = 7,
 * 所求解集为:
 * [
 * ⁠ [7],
 * ⁠ [2,2,3]
 * ]
 *
 *
 * 示例 2:
 *
 * 输入: candidates = [2,3,5], target = 8,
 * 所求解集为:
 * [
 * [2,2,2,2],
 * [2,3,3],
 * [3,5]
 * ]
 *
 */
func combinationSum(candidates []int, target int) [][]int {
	sort.Ints(candidates)

	ans := make([][]int, 0)
	n := len(candidates)
	var backtrack func(int, int, []int)
	backtrack = func(idx, sum int, res []int) {
		if sum < 0 || idx == n {
			return
		}
		if sum == 0 {
			tmp := make([]int, len(res))
			copy(tmp, res)
			ans = append(ans, tmp)
			fmt.Println(ans)
			return
		}
		for i := idx; i < n; i++ {
			backtrack(i, sum-candidates[i], append(res, candidates[i]))
		}
	}
	// fmt.Println(ans)

	backtrack(0, target, []int{})

	return ans
}