08-两数之和（四种解法）

        两数之和1：给定一个整数数组num，从数组中找出两个数满足相加之和等于目标数target。假设每个输入只对应唯一的答案，而且不可以重塑使用相同的元素。返回两数的下标值，以数组形式返回。

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class demo01 {
    
    //使用for循环
    public static int[] equal(int[] nums){
        System.out.println("请输入目标数：");
        Scanner sc = new Scanner(System.in);
        int target = sc.nextInt();
        for (int i = 0; i < nums.length; i++){
            for (int j = i + 1; j < nums.length; j++){
                if (nums[i]+nums[j]==target){
                    return new int[]{i,j};
                }
            }
        }
        return new int[0];
    }
    
    //使用map方法
    public static int[] equal1(int[] nums){
        System.out.println("请输入目标数：");
        Scanner sc = new Scanner(System.in);
        int target = sc.nextInt();
        Map map = new HashMap();
        for (int i = 0; i < nums.length; i++){
            if (map.containsKey(target - nums[i])){
                return new int[]{map.get(target - nums[i]),i};
            }
            map.put(nums[i],i);
        }
     return new int[0];
    }
    public static void main(String[] args) {
        System.out.println(Arrays.toString(equal(new int[]{1,2,3,4,5,6})));
        System.out.println(Arrays.toString(equal1(new int[]{1,2,3,4,5,6})));
    }
}

        两数之和2：给定一个升序排列的整数数组num，从数组中找出两个数满足相加之和等于目标数target。假设每个输入只对应唯一的答案，而且不可以重塑使用相同的元素。返回两数的下标值，以数组形式返回。

import java.util.Arrays;

public class demo01 {
    
    //使用二分查找法
    public static int[] binarySearch(int[] nums, int target){
       for (int i = 0; i < nums.length; i++){
           int low = i,high = nums.length-1;
           while (low<=high){
               int mid = (low+high)/2;
               if (nums[mid]==target-nums[i]){
                   return new int[]{i,mid};//返回一个数组
               }else if (nums[mid]>target-nums[i]){
                   high = mid-1;
               }else{
                   low = mid+1;
               }
           }
       }
     return new int[]{};
    }
    
    //使用双指针法
    public static int[] twopoint(int[] nums, int target){
        int low = 0,high = nums.length-1;
        while (low<=high){
            int sum=nums[low]+nums[high];
            if (sum==target){
                return new int[]{low,high};
            }else if (sum>target){
                high--;
            }else {
                low++;
            }
        }
        return new int[]{0};
    }
    public static void main(String[] args) {
        System.out.println(Arrays.toString(binarySearch(new int[]{1,2,3,4,5,6},10)));
        System.out.println(Arrays.toString(twopoint(new int[]{1,2,3,4,5,6},10)));
    }
}