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.

var results [][]int
var existed map[string]int
func combinationSum(candidates []int, target int) [][]int {
    results = make([][]int, 0)
    if len(candidates) == 0 {
        return results
    }
    existed = make(map[string]int)
    sort.Ints(candidates)
    backtrack(candidates, target, nil)
    return results
}

func backtrack(candidates []int, target int, result []int){
    for _,val := range candidates {
        if val == target {
            result = append(result, val)
            addIfNotExist(result)
            break
        }
        if val < target {
            result = append(result, val)
            backtrack(candidates, target - val, result)
            result = result[0:len(result) - 1]
            continue
        }
        if val > target {
            break
        }
    }
}

func addIfNotExist(result []int){
    var cr []int
    for _,val := range result {
        cr = append(cr, val)
    }
    sort.Ints(cr)
    var s string = ""
    for _, val := range cr {
        s += "," + string(val)
    }
    if _,ok := existed[s];ok {
        return
    }
    results = append(results, cr)
    existed[s] = 1
}