题目一：找出数组中重复的数字。

。。。。。。S₂

。。。。。

 1 class Solution {
 2 public:
 3     // Parameters:
 4     //        numbers:     an array of integers
 5     //        length:      the length of array numbers
 6     //        duplication: (Output) the duplicated number in the array number
 7     // Return value:       true if the input is valid, and there are some duplications in the array number
 8     //                     otherwise false
 9     bool duplicate(int numbers[], int length, int* duplication) {
10         if (numbers == nullptr || length <= 0){
11             return false;
12         }
13
14
15         for (int i = 0; i < length;i++){
16             if (numbers[i] < 0 || numbers[i] >= length){
17                 return false;
18             }
19         }
20
21
22         for (int i=0; i < length; i++){
23             while(numbers[i] != i){
24                 if ( numbers[i] == numbers[numbers[i]]){
25                     *duplication = numbers[i];
26                     return true;
27                 }
28                 int temp;
29                 temp = numbers[numbers[i]];
30                 numbers[numbers[i]] = numbers[i];
31                 numbers[i] = temp;
32             }
33         }
34         return false;
35     }
36 };

原文地址：https://www.cnblogs.com/shiganquan/p/9280891.html