JZ-C-30

剑指offer第三十题：最小的k个数

//============================================================================
// Name        : JZ-C-30.cpp
// Author      : Laughing_Lz
// Version     :
// Copyright   : All Right Reserved
// Description : 最小的k个数
//============================================================================

#include <iostream>
#include <stdio.h>
#include <set>
#include <vector>
#include "Array.h"
using namespace std;

using namespace std;

// ====================方法1:同样可利用分治法====================
void GetLeastNumbers_Solution1(int* input, int n, int* output, int k)
{
    if(input == NULL || output == NULL || k > n || n <= 0 || k <= 0)
        return;

    int start = 0;
    int end = n - 1;
    int index = Partition(input, n, start, end);
    while(index != k - 1)
    {
        if(index > k - 1)
        {
            end = index - 1;
            index = Partition(input, n, start, end);
        }
        else
        {
            start = index + 1;
            index = Partition(input, n, start, end);
        }
    }

    for(int i = 0; i < k; ++i)
        output[i] = input[i];//查找后，放入output数组
}

// ====================方法2:堆、红黑树：set、multiset都是基于红黑树实现的====================
typedef multiset<int, greater<int> >            intSet;
typedef multiset<int, greater<int> >::iterator  setIterator;

void GetLeastNumbers_Solution2(const vector<int>& data, intSet& leastNumbers, int k)
{
    leastNumbers.clear();

    if(k < 1 || data.size() < k)
        return;

    vector<int>::const_iterator iter = data.begin();
    for(; iter != data.end(); ++ iter)
    {
        if((leastNumbers.size()) < k)
            leastNumbers.insert(*iter);

        else
        {
            setIterator iterGreatest = leastNumbers.begin();

            if(*iter < *(leastNumbers.begin()))
            {
                leastNumbers.erase(iterGreatest);
                leastNumbers.insert(*iter);
            }
        }
    }
}

// ====================测试代码====================
void Test(char* testName, int* data, int n, int* expectedResult, int k)
{
    if(testName != NULL)
        printf("%s begins: \n", testName);

    vector<int> vectorData;
    for(int i = 0; i < n; ++ i)
        vectorData.push_back(data[i]);

    if(expectedResult == NULL)
        printf("The input is invalid, we don't expect any result.\n");
    else
    {
        printf("Expected result: \n");
        for(int i = 0; i < k; ++ i)
            printf("%d\t", expectedResult[i]);
        printf("\n");
    }

    printf("Result for solution1:\n");
    int* output = new int[k];
    GetLeastNumbers_Solution1(data, n, output, k);
    if(expectedResult != NULL)
    {
        for(int i = 0; i < k; ++ i)
            printf("%d\t", output[i]);
        printf("\n");
    }

    delete[] output;

    printf("Result for solution2:\n");
    intSet leastNumbers;
    GetLeastNumbers_Solution2(vectorData, leastNumbers, k);
    printf("The actual output numbers are:\n");
    for(setIterator iter = leastNumbers.begin(); iter != leastNumbers.end(); ++iter)
        printf("%d\t", *iter);
    printf("\n\n");
}

// k小于数组的长度
void Test1()
{
    int data[] = {4, 5, 1, 6, 2, 7, 3, 8};
    int expected[] = {1, 2, 3, 4};
    Test("Test1", data, sizeof(data) / sizeof(int), expected, sizeof(expected) / sizeof(int));
}

// k等于数组的长度
void Test2()
{
    int data[] = {4, 5, 1, 6, 2, 7, 3, 8};
    int expected[] = {1, 2, 3, 4, 5, 6, 7, 8};
    Test("Test2", data, sizeof(data) / sizeof(int), expected, sizeof(expected) / sizeof(int));
}

// k大于数组的长度
void Test3()
{
    int data[] = {4, 5, 1, 6, 2, 7, 3, 8};
    int* expected = NULL;
    Test("Test3", data, sizeof(data) / sizeof(int), expected, 10);
}

// k等于1
void Test4()
{
    int data[] = {4, 5, 1, 6, 2, 7, 3, 8};
    int expected[] = {1};
    Test("Test4", data, sizeof(data) / sizeof(int), expected, sizeof(expected) / sizeof(int));
}

// k等于0
void Test5()
{
    int data[] = {4, 5, 1, 6, 2, 7, 3, 8};
    int* expected = NULL;
    Test("Test5", data, sizeof(data) / sizeof(int), expected, 0);
}

// 数组中有相同的数字
void Test6()
{
    int data[] = {4, 5, 1, 6, 2, 7, 2, 8};
    int expected[] = {1, 2};
    Test("Test6", data, sizeof(data) / sizeof(int), expected, sizeof(expected) / sizeof(int));
}

// 输入空指针
void Test7()
{
    int* expected = NULL;
    Test("Test7", NULL, NULL, expected, 0);
}

int main(int argc, char** argv)
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();
    Test6();
    Test7();

    return 0;
}

关于Partition方法：

// 《剑指Offer——名企面试官精讲典型编程题》代码
// 著作权所有者：何海涛

#include <stdlib.h>
#include <stdio.h>
#include "Array.h"
#include <exception>

// Random Partition
int RandomInRange(int min, int max) {
    int random = rand() % (max - min + 1) + min;
    return random;
}

void Swap(int* num1, int* num2) {
    int temp = *num1;
    *num1 = *num2;
    *num2 = temp;
}

int Partition(int data[], int length, int start, int end) {
    if (data == NULL || length <= 0 || start < 0 || end >= length) {
        printf("Invalid Parameters");
        throw new std::exception();//这里括号里为什么不能加msg？？？！！！
    }
    int index = RandomInRange(start, end);
    Swap(&data[index], &data[end]);

    int small = start - 1;
    for (index = start; index < end; ++index) {
        if (data[index] < data[end]) {
            ++small;
            if (small != index)
                Swap(&data[index], &data[small]);
        }
    }

    ++small;
    Swap(&data[small], &data[end]);

    return small;
}