POJ 1009--Edge Detection

最新推荐文章于 2019-08-15 17:09:57 发布

Hering_Linux

最新推荐文章于 2019-08-15 17:09:57 发布

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分类专栏： C++/C POJ解题报告文章标签： poj

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本文介绍了一种用于计算图片边界的算法实现。通过分析点的位置来确定哪些点需要被计算，并利用STL容器优化计算过程。文章提供了完整的C++代码示例。

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题意

简单的讲，题目的意思就是计算一张图片的边界。

分析

首先，不可能每个点挨个计算，所以要找出哪些需要计算的点。
使用了STL容器，另外加上情况考虑得比较复杂，所以效率不高。

代码如下：

#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
void  ComputePoint(vector<int>& Result, const int& Point, const int& Width, const int& EndPoint, const int Key)
{
    if (Point - Width >= 0)
    {
        Result.push_back(Point - Width);
        if ((Point - Width) % Width > 0)    Result.push_back(Point - Width - 1);
        if ((Point - Width) % Width < Width - 1)    Result.push_back(Point - Width + 1);
        if (Key == 1 && (Point - Width) % Width == Width - 1)   Result.push_back(Point - Width + 1);
    }
    if (Point + Width <= EndPoint)
    {
        Result.push_back(Point + Width);
        if ((Point + Width) % Width > 0)    Result.push_back(Point + Width - 1);
        if ((Point + Width) % Width < Width - 1)    Result.push_back(Point + Width + 1);
        if (Key == 1 && (Point + Width) % Width == Width - 1 && Point + Width + 1 <= EndPoint)  Result.push_back(Point + Width + 1);
    }
    Result.push_back(Point);
    if (Point % Width > 0)  Result.push_back(Point - 1);
    if (Point % Width < Width - 1)  Result.push_back(Point + 1);

};
int Find(const int* ValArray, const int* End, const int Point)
{
    for (int i = 0;; ++i)
        if (Point <= End[i])
            return ValArray[i];
}
int Compare(const vector<int>& Vec, const int Value, const int*ValArray, const int* End)
{
    int temp = 0;
    for (vector<int>::const_iterator iter = Vec.begin(); iter != Vec.end(); ++iter)
        if (Value != *iter&&temp < abs(Find(ValArray, End, *iter) - Find(ValArray, End, Value)))    temp = abs(Find(ValArray, End, *iter) - Find(ValArray, End, Value));
    return temp;
};
void Maximize(const vector<int>& NeedCompute, const int& Width, const int& EndPoint, const int* ValArray, const int* End)
{
    int Count = (int)NeedCompute.size();
    int* List = new int[Count];
    int* Position = new int[Count];
    vector<int>::const_iterator iter = NeedCompute.begin();
    for (int i = 0; iter != NeedCompute.end(); ++iter, ++i)
    {
        Position[i] = *iter;
        vector<int> temp;
        ComputePoint(temp, *iter, Width, EndPoint, 0);
        List[i] = Compare(temp, *iter, ValArray, End);
    }
    cout << Width << endl;
    for (int i = 0; i < Count;)
    {
        int j = i + 1;
        for (; j < Count; ++j)
            if (List[j] != List[i])
            {
                cout << List[i] << " " << Position[j] - Position[i] << endl;
                i = j;
                break;
            }
        if (j == Count)
        {
            cout << List[i] << " " << EndPoint - Position[i] + 1 << endl;
            break;
        }
    }
    cout << 0 << " " << 0 << endl;
    delete[]List;
    delete[]Position;
}
void Calculate(const int& Width, const int& Length, const int* ValArray, const int* Start, const int* End)
{
    vector<int> NeedCompute;
    for (int i = 0; i < Length; i++)
    {
        ComputePoint(NeedCompute, Start[i], Width, End[Length - 1], 1);
        NeedCompute.push_back(Start[i] - (Start[i] % Width));
    }
    sort(NeedCompute.begin(), NeedCompute.end());
    NeedCompute.erase(unique(NeedCompute.begin(), NeedCompute.end()), NeedCompute.end());
    Maximize(NeedCompute, Width, End[Length - 1], ValArray, End);
}
int main()
{
    int Width;
    while (cin >> Width&&Width != 0)
    {
        int Value = 0;
        int Count = 0;
        int ValArray[1000];
        int Start[1000];
        int End[1000];
        int Length = 0;
        while (cin >> Value >> Count&&Count != 0)
        {
            if (Length == 0)
            {
                Start[Length] = 0;
                End[Length] = Count - 1;
            }
            else
            {
                Start[Length] = End[Length - 1] + 1;
                End[Length] = End[Length - 1] + Count;
            }
            ValArray[Length] = Value;
            ++Length;
        }
        Calculate(Width, Length, ValArray, Start, End);
    }
    cout << 0 << endl;
    return 0;
}