# leetCode 15 和 16 三数之和
## 双指针写法
先预排序，再遍历
## code 15
```go
func threeSum(nums []int) [][]int {
target := 0
res := [][]int{}
L := len(nums)
if L < 3 {
return res
}
sort.Ints(nums)
for index := 0; index < L - 2; index ++ {
if nums[index] > 0 {
break
}
start := index + 1
// 去重
if index > 0 && nums[index] == nums[index - 1] {
continue
}
end := L - 1
for start < end {
if nums[index] + nums[start] + nums[end] < target {
start += 1
// 去重
for nums[start] == nums[start - 1] && start < end {
start += 1
}
} else if nums[index] + nums[start] + nums[end] > target {
end -= 1
// 去重
for nums[end] == nums[end + 1] && start < end {
end -= 1
}
} else {
res = append(res, []int{nums[index], nums[start], nums[end]})
start += 1
end -= 1
// 去重
for nums[start] == nums[start - 1] && nums[end] == nums[end + 1] && start < end {
start += 1
end -= 1
}
}
}
}
return res
}
```
## code 16
```go
func threeSumClosest(nums []int, target int) int {
L := len(nums)
if L == 0 {
return target
}
sort.Ints(nums)
delta := nums[0] + nums[1] + nums[2] - target
for index := 0; index < L - 2; index ++ {
start := index + 1
if index > 0 && nums[index] == nums[index - 1] {
continue
}
end := L - 1
for start < end {
newDelta := nums[index] + nums[start] + nums[end] - target
if newDelta == 0 {
return target
}
if abs(delta) > abs(newDelta) {
delta = newDelta
}
if newDelta < 0 {
start += 1
for nums[start] == nums[start - 1] && start < end {
start += 1
}
} else {
end -= 1
for nums[end] == nums[end + 1] && start < end {
end -= 1
}
}
}
}
return delta + target
}
func abs(num int) int {
if num >= 0 {
return num
} else {
return -1 * num
}
}
```
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