2020-11-07：已知一个正整数数组，两个数相加等于N并且一定存在，如何找到两个数相乘最小的两个数？

福哥答案2020-11-07：

1.哈希法。
2.排序+双指针夹逼。

golang代码如下：

package main
 
import (
    "fmt"
    "sort"
)
 
const INT_MAX = int(^uint(0) >> 1)
 
func main() {
    nums := []int{2, 1, 3, 4, 5, 6, 9, 8, 7}
    fmt.Println(twoSumMultiplication1(nums, 12), "哈希法")
    fmt.Println(twoSumMultiplication2(nums, 12), "排序+双指针夹逼")
}
 
//哈希法
func twoSumMultiplication1(nums []int, target int) int {
    map0 := make(map[int]struct{})
    min := INT_MAX
 
    for i := 0; i < len(nums); i++ {
        complement := target - nums[i]     //差值 = 目标值-元素值
        if _, ok := map0[complement]; ok { //如果字典里有差值，说明已经找到了
            //确保complement是较小的那个值
            if complement > nums[i] {
                complement, nums[i] = nums[i], complement
            }
 
            //谁小保存谁
            if complement < min {
                min = complement
                //如果最小值是1，就不用循环了。
                if min == 1 {
                    break
                }
            }
 
        } else {
            //如果字典里没有差值，缓存数组的当前值
            map0[nums[i]] = struct{}{}
        }
    }
 
    return min
}
 
//排序+双指针夹逼
func twoSumMultiplication2(nums []int, target int) int {
    //排序
    sort.Slice(nums, func(i, j int) bool {
        return nums[i] < nums[j]
    })
 
    sumtemp := 0
    min := INT_MAX
 
    for i, j := 0, len(nums)-1; i < j; {
        sumtemp = nums[i] + nums[j]
        if target == sumtemp {
            if min > nums[i] {
                min = nums[i]
                if min == 1 {
                    break
                }
            }
            i++
        } else if target > sumtemp {
            i++
        } else {
            j--
        }
    }
 
    return min
}