面试题3：数组中重复的数字 ：不修改数组找出重复的数字

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/*******************************************************************
Copyright(c) 2018, htfeng
All rights reserved.
*******************************************************************/

//==================================================================
// 《剑指Offer——名企面试官精讲典型编程题》代码
//  作者：何海涛
//  C++
//==================================================================

// 面试题3：数组中重复的数字
// 题目2：不修改数组找出重复的数字

#include<iostream>

using namespace std;

int countRange(const int* numbers, int length, int start, int end) {
    if (numbers == nullptr)
        return 0;
    int count = 0;
    for (int i = 0; i < length; i++) {
        if (numbers[i] >= start && numbers[i] <= end)
            ++count;
    }
    return count;
}
int getDuplicate(const int *numbers, int length) {
    if (numbers == nullptr || length < 0)
        return -1;

    int start = 1;
    int end = length - 1;
    while (end >= start) {
        int middle = ((end - start) >> 1) + start;
        int count = countRange(numbers, length, start, middle);
        if (end == start) {
            if (count > 1)
                return start;
            else
                break;
        }

        if (count > (middle - start + 1))
            end = middle;
        else
            start = middle + 1; 
    }
    return -1;
}
//=========================test=====================================
// 长度为n的数组里包含一个或多个重复的数字
void test1() {
    int numbers[] = { 2, 3, 1, 0, 2, 5, 3 };
    int length = sizeof(numbers) / sizeof(int);
    int result =getDuplicate(numbers, length);
    cout << result << endl;
}

// 数组里不包含重复的数字
void test2() {
    int numbers[] = { 2, 3, 1, 0, 5 };
    int length = sizeof(numbers) / sizeof(int);
    int result = getDuplicate(numbers, length);
    cout << result << endl;
}

// 无效的输入用例
void test3() {
    int* numbers = nullptr;
    int length = sizeof(numbers) / sizeof(int);
    int result = getDuplicate(numbers, length);
    cout << result << endl;
}

int main() {
    test1();
    test2();
    test3();
    system("pause");
    return 0;
}