排序子序列（牛客）

目录

一、题目

二、代码

（一）时间复杂度过高（通过70%）

（二）改进 

---

一、题目

二、代码

（一）时间复杂度过高（通过70%）

#include 
#include 
#include
using namespace std;

bool ASC(vectora, int begin, int end)
{ //升序
    if (begin == end)
        return true;
    for (int k = begin + 1; k <= end; k++)
    {
        if (a[k] >= a[k - 1])
        {
            continue;
        }
        else
        {
            return false;
        }
    }
    return true;
}


bool DESC(vectora, int begin, int end)
{ //降序
    if (begin == end)
        return true;
    for (int k = begin + 1; k <= end; k++)
    {
        if (a[k] <= a[k - 1])
        {
            continue;
        }
        else
        {
            return false;
        }
    }
    return true;
}
int main() {
    int n;
    cin >> n;
    vectordata;
    int x;
    for (int i = 0; i < n; i++) {
        cin >> x;
        data.push_back(x);
    }

    int sum = 0;
    int start = 0, oldstart = -1;
    int prev = 0;
    int next = 0;
    while (next <= n - 1)
    {
        if (ASC(data, start, next) || DESC(data, start, next))
        {
            prev = next;
            ++next;
            continue;
        }

        if (start != oldstart)
        {
            sum += 1;
            oldstart = start;
            start = next;
        }

    }
    if (start != oldstart)
    {
        sum += 1;
    }

    cout << sum;
    return 0;
}

（二）改进 

•  主要是将判断升序和降序的代码合并成了一个！！！

bool isSort(vector& a, int begin, int end, bool increasing) 
{
    if (begin == end) 
        return true;
    for (int k = begin + 1; k <= end; k++) 
    {
        if (increasing) //升序
        {
            if (a[k] >= a[k - 1]) 
                continue;
            else 
                return false;
        }
        else //降序
        {
            if (a[k] <= a[k - 1]) 
                continue;
            else 
                return false;
        }
    }
    return true;
}

完整代码

#include 
#include 
#include 
using namespace std;

bool isSort(vector& a, int begin, int end, bool increasing) 
{
    if (begin == end) 
        return true;
    for (int k = begin + 1; k <= end; k++) 
    {
        if (increasing) //升序
        {
            if (a[k] >= a[k - 1]) 
                continue;
            else 
                return false;
        }
        else //降序
        {
            if (a[k] <= a[k - 1]) 
                continue;
            else 
                return false;
        }
    }
    return true;
}

int main() {
    int n;
    cin >> n;
    vector data;
    int x;
    for (int i = 0; i < n; i++) 
    {
        cin >> x;
        data.push_back(x);
    }

    int sum = 0;
    int start = 0, oldstart = -1;//oldstart用于表示上一次有序子序列开始的下标
    int prev = 0;
    int next = 0;

    while (next <= n - 1) 
    {
        if (isSort(data, start, next, true) || isSort(data, start, next, false)) 
        {
            prev = next;
            ++next;
            continue;
        }

        if (start != oldstart) {
            sum += 1;
            oldstart = start;
            start = next;
        }
    }

    if (start != oldstart) //跳出循环，最后一个子序列的判断
    {
        sum += 1;
    }

    cout << sum;
    return 0;
}