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判断能否形成等差数列 - 简单

news 来源：原创 2025/5/19 21:00:31

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C++

topic: 1502. 判断能否形成等差数列 - 力扣（LeetCode）

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Have a slight inspect at the topic.

Sort first when I give the topic first eye. Sort is a standard library in c++. This basic use of sort is really easy.

int arr[] = {4, 2, 5, 1};
sort(arr.begin(), arr.end()); // 结果：{1, 2, 4, 5}

vector<int> vec = {4, 2, 5, 1};
sort(vec.begin(), vec.end()); // 结果：{1, 2, 4, 5}

Sort by default ranks from small to big. If you want to range the elements from big to small, do something.

// 降序排序
sort(vec.begin(), vec.end(), greater<int>());

class Solution {
public:
    bool canMakeArithmeticProgression(vector<int>& arr) {

        // sort the vector first
        sort(arr.begin(), arr.end());

        int n = arr.size();

        // calculater the difference
        int a = arr[1] - arr[0];

        for (int i = 1; i < n; ++i)
        {
            if (arr[i] - arr[i - 1] == a)
            {
                return true;
            }
            else
            {
                
            }
        }
        
        return false;
    }
};

But you gays guess what.

I dont know where is wrong. Run the program manually.

步骤	当前执行代码行	变量状态变化	条件判断结果	循环迭代次数	输出内容	操作注释
1	`sort(arr.begin(), arr.end());`	`arr` → <span style=‘color:red’>[1,2,4]</span>	无	无	无	对数组进行升序排序
2	`int n = arr.size();`	`n` → <span style=‘color:red’>3</span>	无	无	无	获取数组长度
3	`int a = arr[1] - arr[0];`	`a` → <span style=‘color:red’>1</span>	无	无	无	计算初始差值（假设为公差）
4	`for (int i = 1; i < n; ++i)`	`i` → <span style=‘color:red’>1</span>	`i < 3` → true	第1次迭代	无	进入循环，检查公差一致性
5	`if (arr[i] - arr[i-1] == a)`	无	条件成立	无	无	差值等于初始公差 `a=1`
6	`return true;`	无	无	无	true	立即返回 `true`，函数终止

OK, that make sense.

class Solution {
public:
    bool canMakeArithmeticProgression(vector<int>& arr) 
    {
        sort(arr.begin(), arr.end());
        int n = arr.size();
        int diff = arr[1] - arr[0]; // 记录标准差值

        // 从第2个元素开始检查所有相邻对
        for (int i = 2; i < n; ++i) 
        {  // 注意i从2开始
            if (arr[i] - arr[i-1] != diff) 
            {
                return false;
            }
        }
        
        return true; // 全部符合条件
    }
};