Page Comparison

// nums should be already sorted
func nSum(nums []int, target int, n int) (results [][]int) {
    if n == 2 {
        return twoSum(nums, target)
    }

    i := 0
    for i < len(nums)-n+1 {
        partResults := nSum(nums[i+1:], target-nums[i], n-1)
        for _, r := range partResults {
            results = append(results,
              append([]int{nums[i]}, r...),
            )
        }

        for v := nums[i]; i < len(nums)-n+1 && nums[i] == v; i++ {}
    }

    return
}

func twoSum(nums []int, target int) (results [][]int) {
    i, j := 0, len(nums)-1
    for i < j {
        sum := nums[i] + nums[j]
        if sum == target {
            results = append(results, []int{nums[i], nums[j]})

            for v := nums[i]; i < len(nums) && nums[i] == v; i++ {}
            for v := nums[j]; j >= 0 && nums[j] == v; j-- {}
        } else if sum < target {
            for v := nums[i]; i < len(nums) && nums[i] == v; i++ {}
        } else {
            for v := nums[j]; j >= 0 && nums[j] == v; j-- {}
        }
    }
    return 
}

// 使用示例（利用 4Sum）做演示
func fourSum(nums []int, target int) (results [][]int) {
    sort.Ints(nums)

    return nSum(nums, target, 4)
}