[Algorithm learning] Given an integer array, find two integers for the specified integer and (1)

Question description: Given an integer array, is it possible to find out two of them and make them a specified value? (assumed to be unordered arrays)

Solution One: Brute force (exhaustive method, not advocated)

  
 

   
  

  
 /**
   
  

  
 * 暴力破解
   
  

  
 * (穷举，时间复杂度：O(n^2)，正常是不会用这个滴，假如只是为了快速解题，对时间没有限制，用这个最简单)
   
  

  
 *
   
  

  
 * @param nums
   
  

  
 * @param target
   
  

  
 */
   
  

  
 public static void findTwo1(int[] nums, int target)
   
  

  
 {
   
  

  
 int one, two;
   
  

  
 for (int i = 0; i < nums.length; i++)
   
  

  
 {
   
  

  
 one = nums[i];
   
  

  
 two = target - one;
   
  

  
 for (int j = 0; j < nums.length; j++)
   
  

  
 {
   
  

  
 if (i != j)
   
  

  
 {
   
  

  
 if (two == nums[j])
   
  

  
 {
   
  

  
 System.out.println("one:" + one + " two:" + two);
   
  

  
 return;
   
  

  
 }
   
  

  
 }
   
  

  
 }
   
  

  
 }
   
  

  
 System.out.println("找不到这两个数");
   
  

  
 }
  
 

Solution 2:2 Method (equivalent to two pointers)

  
 

   
  

  
 /**
   
  

  
 * 两个指针二分查找
   
  

  
 * (排序时间复杂度为O(nlog(n)),while最多O(N)，所以最终程序的时间复杂度为：O(nlo(n)))
   
  

  
 *
   
  

  
 * @param nums
   
  

  
 * @param target
   
  

  
 */
   
  

  
 public static void findTwo2(int[] nums, int target)
   
  

  
 {
   
  

  
 // 1.排列（用的是Dual-Pivot Quicksort(快速排序),时间复杂度为O(nlog(n))）
   
  

  
 Arrays.sort(nums);
   
  

  
 // 2.类二分查找
   
  

  
 int left = 0;
   
  

  
 int right = nums.length - 1;
   
  

  
 while (left < right)
   
  

  
 {
   
  

  
 if (nums[left] + nums[right] > target)
   
  

  
 {// 太大 right减少
   
  

  
 right--;
   
  

  
 }
   
  

  
 else if (nums[left] + nums[right] < target)
   
  

  
 {// 太小left增加
   
  

  
 left++;
   
  

  
 }
   
  

  
 else
   
  

  
 {// 找到结果，结束查找
   
  

  
 System.out.println("one:" + nums[left] + " two:" + nums[right]);
   
  

  
 return;
   
  

  
 }
   
  

  
 }
   
  

  
 System.out.println("找不到这两个数");
   
  

  
 }
  
 

From for notes (Wiz)

[Algorithm learning] Given an integer array, find two integers for the specified integer and (1)