【剑指Offer】42、和为S的两个数字

 1  /*假设：若b>a,且存在，
 2 a + b = s;
 3 (a - m ) + (b + m) = s
 4 则：(a - m )(b + m)=ab - (b-a)m - m*m < ab；说明外层的乘积更小*/
 5 //mine
 6 public static  ArrayList<Integer> FindNumbersWithSum(int[] array, int sum) {
 7         ArrayList<Integer> list = new ArrayList<>();
 8          if (array == null || array.length == 0)
 9             return list;
10         for (int i = 0; i <array.length-1; i++) {
11             for (int j = array.length-1; j >=i; j--) {
12                 if (array[j] == (sum - array[i])) {
13                     list.add(array[i]);
14                     list.add(array[j]);
15                     return list;
16                 }
17             }
18         }
19         return list;
20     }
21 //讨论题解
22     public static ArrayList<Integer> FindNumbersWithSum02(int[] array, int sum) {
23         ArrayList<Integer> list = new ArrayList<>();
24         if (array == null || array.length == 0)
25             return list;
26         int left = 0;
27         int right = array.length - 1;
28         while (left < right) {
29             int total = array[left] + array[right];
30             if (total == sum) {
31                 list.add(array[left]);
32                 list.add(array[right]);
33                 return list;
34             } else if (total > sum) {
35                 //大于sum，说明太大了，right左移寻找更小的数
36                 --right;
37 
38             } else {
39                 //2.如果和小于sum，说明太小了，left右移寻找更大的数
40                 ++left;
41             }
42         }
43         return list;
44     }

1  public static void main(String[] args) {
2         ArrayList<Integer> arrayList = new ArrayList<Integer>();
3         int[] array = {0,1, 4, 6, 9,10, 15, 20, 22, 23};
4         int sum = 10;
5         arrayList = FindNumbersWithSum(array, sum);
6         //arrayList = FindNumbersWithSum02(array, sum);
7         System.out.println(arrayList);
8     }