题目:
题解:
func fourSum(nums []int, target int) (quadruplets [][]int) {
sort.Ints(nums)
n := len(nums)
for i := 0; i < n-3 && nums[i]+nums[i+1]+nums[i+2]+nums[i+3] <= target; i++ {
if i > 0 && nums[i] == nums[i-1] || nums[i]+nums[n-3]+nums[n-2]+nums[n-1] < target {
continue
}
for j := i + 1; j < n-2 && nums[i]+nums[j]+nums[j+1]+nums[j+2] <= target; j++ {
if j > i+1 && nums[j] == nums[j-1] || nums[i]+nums[j]+nums[n-2]+nums[n-1] < target {
continue
}
for left, right := j+1, n-1; left < right; {
if sum := nums[i] + nums[j] + nums[left] + nums[right]; sum == target {
quadruplets = append(quadruplets, []int{nums[i], nums[j], nums[left], nums[right]})
for left++; left < right && nums[left] == nums[left-1]; left++ {
}
for right--; left < right && nums[right] == nums[right+1]; right-- {
}
} else if sum < target {
left++
} else {
right--
}
}
}
}
return
}