算法导论9.2以期望线性时间做选择

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#include <stdint.h>
#include <time.h>
#include <iostream>
#ifdef __linux
#include <stdio.h>
#include <stdlib.h>
#endif

void swap(int64_t* A, uint64_t i, uint64_t j)
{
    int64_t tmp = A[i];
    A[i] = A[j];
    A[j] = tmp;
}

int64_t partition(int64_t* A, int64_t p, int64_t r)
{
    int64_t x = A[r];
    int64_t i = p;
    for (int64_t j = p; j < r; j++)
    {
        if (A[j] <= x)
        {
            swap(A, i, j);
            i++;
        }
    }
    swap(A, i, r);
    return i;
}

int64_t RandomizedPartition(int64_t* A, int64_t p, int64_t r)
{
    int64_t i = (rand() % (r - p)) + p;
    swap(A, i, r);
    return partition(A, p, r);
}

// RANDOMIZED-SELECT(A, p, r, i)
// if p == r
//     return A[p]
// q = RANDOMIZED-PARTITION(A, p, r)
// k = q - p + 1
// if i == k
// return A[q]
// else if i < k
//     return RANDOMIZED-SELECT(A, p, q - 1, i)
// else
//     return RANDOMIZED-SELECT(A, q + 1, r, i - k)

int64_t RandomizedSelect(int64_t* A, int64_t p, int64_t r, int64_t i)
{
    if (p == r)
    {
        return A[p];
    }
    int64_t q = RandomizedPartition(A, p, r);
    int64_t k = q - p + 1;
    if (i == k)
    {
        return A[q];
    }
    else if (i < k)
    {
        return RandomizedSelect(A, p, q - 1, i);
    }
    else
    {
        return RandomizedSelect(A, q + 1, r, i - k);
    }
}
int main()
{
    int64_t array[] = { 2, 8, 7, 1, 3, 5, 6, 4 };
    
    std::cout << RandomizedSelect(array, 0, 7, 3) << std::endl;
    getchar();
    return 0;
}

BIN     = bin
FMCSA   = find_max_crossing_subarray
IAS     = IA_solution
IST     = insertion_sort_t
LMSA    = liner_time_max_subarray
MERGE   = merge
MERGE_T = merge_t
VMS     = violate_max_subarray
STRA    = 4.2_strassen
COUNT_SORT = 8.2_counting_sort
MINIMUMMAXIMUM = 9.1_MinimumMaximum
RS = 9.2_RandomizedSelect
RQ = 7.3_RandomizedQuicksort
QS = 7.1_quicksort

CFLAGS = -g -Wall

all : ${BIN}/${COUNT_SORT} ${BIN}/${RS} ${BIN}/${QS} ${BIN}/${FMCSA} ${BIN}/${RQ} ${BIN}/${IAS} ${BIN}/${IST} ${BIN}/${LMSA} ${BIN}/${MERGE} ${BIN}/${MERGE_T} ${BIN}/${VMS} ${BIN}/${STRA} ${BIN}/${MINIMUMMAXIMUM}

${BIN}/${COUNT_SORT} : ${COUNT_SORT}/counting_sort.cpp
	g++ ${COUNT_SORT}/counting_sort.cpp ${CFLAGS} -o ${BIN}/${COUNT_SORT}

${BIN}/${FMCSA} : ${FMCSA}/main.cpp ${FMCSA}/max_sub_array.h
	g++ ${FMCSA}/main.cpp ${CFLAGS} -o ${BIN}/${FMCSA}

${BIN}/${IAS} : ${IAS}/insertion_sort.cpp ${IAS}/insertion_sort.h
	g++ ${IAS}/insertion_sort.cpp ${CFLAGS} -o ${BIN}/${IAS}

${BIN}/${IST} : ${IST}/${IST}.cpp ${IST}/${IST}.h
	g++ ${IST}/${IST}.cpp ${CFLAGS} -o ${BIN}/${IST}

${BIN}/${LMSA} : ${LMSA}/Source.cpp
	g++ ${LMSA}/Source.cpp ${CFLAGS} -o ${BIN}/${LMSA}

${BIN}/${MERGE} : ${MERGE}/${MERGE}.cpp  ${MERGE}/${MERGE}.h
	g++ -std=c++0x ${MERGE}/${MERGE}.cpp ${CFLAGS} -o ${BIN}/${MERGE}

${BIN}/${MERGE_T} : ${MERGE_T}/${MERGE_T}.cpp  ${MERGE_T}/${MERGE_T}.h
	g++ -std=c++0x ${MERGE_T}/${MERGE_T}.cpp ${CFLAGS} -o ${BIN}/${MERGE_T}

${BIN}/${VMS} : ${VMS}/Source.cpp
	g++ ${VMS}/Source.cpp ${CFLAGS} -o ${BIN}/${VMS}

${BIN}/${STRA} : ${STRA}/strassen.cpp ${STRA}/strassen.h
	g++ -std=c++0x ${STRA}/strassen.cpp ${CFLAGS} -o ${BIN}/${STRA}

${BIN}/${MINIMUMMAXIMUM} : ${MINIMUMMAXIMUM}/${MINIMUMMAXIMUM}.cpp
	g++ ${MINIMUMMAXIMUM}/${MINIMUMMAXIMUM}.cpp ${CFLAGS} -o ${BIN}/${MINIMUMMAXIMUM}
	
${BIN}/${RS} : ${RS}/${RS}.cpp
	g++ ${RS}/${RS}.cpp ${CFLAGS} -o ${BIN}/${RS}

${BIN}/${RQ} : ${RQ}/${RQ}.cpp
	g++ ${RQ}/${RQ}.cpp ${CFLAGS} -o ${BIN}/${RQ}
	
${BIN}/${QS} : ${QS}/${QS}.cpp ${QS}/${QS}.h
	g++ ${QS}/${QS}.cpp ${CFLAGS} -o ${BIN}/${QS}

clean:
	rm ${BIN}/*

算法导论9.2以期望线性时间做选择

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原文地址：http://www.cnblogs.com/sunyongjie1984/p/4283278.html