// 面试题53（三）：数组中数值和下标相等的元素
// 题目：假设一个单调递增的数组里的每个元素都是整数并且是唯一的。请编程实
// 现一个函数找出数组中任意一个数值等于其下标的元素。例如，在数组{-3, -1,
// 1, 3, 5}中，数字3和它的下标相等。//思想：因为这里也是递增的，如果中间点的值大于下标，那后面所有值都会大于相应下标，同理中间点小于下标，前面都会小于下标
#include <iostream>int GetNumberSameAsIndex(const int* numbers, int length)
{if (numbers == nullptr || length <= 0)return -1;int left = 0;int right = length - 1;while (left <= right){int middle = left + ((right - left) >> 1);if (numbers[middle] == middle)//第一种情况，中间点直接中了return middle;if (numbers[middle] > middle)//第二种情况，中间点值大于坐标，向左区间找right = middle - 1;else//第三种情况，中间点值小于坐标，向右区间找left = middle + 1;}return -1;
}// ====================测试代码====================
void Test(const char* testName, int numbers[], int length, int expected)
{if (GetNumberSameAsIndex(numbers, length) == expected)printf("%s passed.\n", testName);elseprintf("%s FAILED.\n", testName);
}void Test1()
{int numbers[] = { -3, -1, 1, 3, 5 };int expected = 3;Test("Test1", numbers, sizeof(numbers) / sizeof(int), expected);
}void Test2()
{int numbers[] = { 0, 1, 3, 5, 6 };int expected = 0;Test("Test2", numbers, sizeof(numbers) / sizeof(int), expected);
}void Test3()
{int numbers[] = { -1, 0, 1, 2, 4 };int expected = 4;Test("Test3", numbers, sizeof(numbers) / sizeof(int), expected);
}void Test4()
{int numbers[] = { -1, 0, 1, 2, 5 };int expected = -1;Test("Test4", numbers, sizeof(numbers) / sizeof(int), expected);
}void Test5()
{int numbers[] = { 0 };int expected = 0;Test("Test5", numbers, sizeof(numbers) / sizeof(int), expected);
}void Test6()
{int numbers[] = { 10 };int expected = -1;Test("Test6", numbers, sizeof(numbers) / sizeof(int), expected);
}void Test7()
{Test("Test7", nullptr, 0, -1);
}int main(int argc, char* argv[])
{Test1();Test2();Test3();Test4();Test5();Test6();Test7();system("pause");return 0;
}