0

该代码适用于 small num_items，但会溢出堆栈num_items = 1000。

我认为 1000 是一个很小的数字，因此应该有一种方法可以使这项工作达到更大的数字。我该怎么做才能让它在更多的递归调用中存活下来？

#include <iostream>
#include <algorithm>
#include <vector>
#include <cstdlib>
#include <ctime>

void printv(std::vector<int>& v) {
    for (int i=0; i<v.size(); i++) std::cout << v[i] << " ";
    std::cout << std::endl;
}

void quicksort(std::vector<int>& v, int begin, int end) {

    if (((end - begin) <= 1) ||
        (begin < 0) ||
        (end > (v.size() - 1))) return;

    int pivot = v[std::rand() % v.size()];

    int x = 0;
    int y = v.size() -1;

    while(x < y) {
        int changed = 0;
        if(v[x] <= pivot) {
            x++;
            changed = 1;
        }
        if (v[y] > pivot) {
            y--;
            changed = 1;
        }
        if (!changed){
            std::swap(v[x], v[y]);
            x++;
            y--;
        }
    }

    if (x == y) y++;
    if (x > y) std::swap(x, y);

    quicksort(v, begin, x);
    quicksort(v, y, end);
}

int ran() {
    return std::rand() % 100;
}

int main() {
    std::srand(std::time(0));
    int num_items = 1000;
    std::vector<int> v (num_items);
    std::generate_n(v.begin(), num_items, ran);

    printv(v);
    quicksort(v, 0, v.size()-1);
    printv(v);
}

也欢迎对代码进行一般评论。

卡在[0,4]：

#1  0x0000000000400b4c in quicksort (
    v=std::vector of length 1000, capacity 1000 = {...}, begin=0, end=4)
    at quicksort.cpp:14
#2  0x0000000000400cc1 in quicksort (
    v=std::vector of length 1000, capacity 1000 = {...}, begin=0, end=4)
    at quicksort.cpp:43
#3  0x0000000000400cc1 in quicksort (
    v=std::vector of length 1000, capacity 1000 = {...}, begin=0, end=4)
    at quicksort.cpp:43
#4  0x0000000000400cc1 in quicksort (
    v=std::vector of length 1000, capacity 1000 = {...}, begin=0, end=4)
    at quicksort.cpp:43
#5  0x0000000000400cc1 in quicksort (
    v=std::vector of length 1000, capacity 1000 = {...}, begin=0, end=4)
    at quicksort.cpp:43
#6  0x0000000000400cc1 in quicksort (
    v=std::vector of length 1000, capacity 1000 = {...}, begin=0, end=4)
    at quicksort.cpp:43
#7  0x0000000000400cc1 in quicksort (
    v=std::vector of length 1000, capacity 1000 = {...}, begin=0, end=4)
    at quicksort.cpp:43
4

1 回答 1

3 
int pivot = v[std::rand() % v.size()];

int x = 0;
int y = v.size() -1;

您显式传递begin和end定位，但您从完整列表中选择枢轴元素。这听起来不对。begin您应该在和之间选择一个枢轴元素end。此外，x应该从 开始begin，并且y应该从 开始end。否则，您总是在每个递归步骤中处理完整的列表，这将解释您正在经历的无限递归。

于 2012-10-07T15:05:24.760 回答