POJ-1840 Eqs Hash表

不得不说上次看得的这句话是多么对，再差的Hash表都比map好，hash表的查找速度可不是logn能够比的。

首先将5个部分拆成2+3，我们选取2的部分进行hash，然后再进行3重for循环。

动态申请内存还是比不上静态的啊。

代码如下：

动态申请内存：

#include <cstdio>

#include <cstring>

#include <cstdlib>

#define MOD 20003

using namespace std;



int rec[105];



struct Node

{

    int x;

    Node *next;

}e[20003];



void Hash(int key)

{ 

    Node *p = &e[abs(key)%MOD];

    Node *q = new Node;

    q->x = key;

    q->next = p->next;

    p->next = q;

}



int find(int key)

{

    int ans = 0;

    Node *p = &e[abs(key) % MOD];

    while (p != NULL) {

        if (p->x == key) {

            ++ans;

        }

        p = p->next;

    }

    return ans;

}



int main()

{

    int a, b, c, d, e, ans, x; 

    for (int i = -50; i <= 50; ++i) {

        rec[i+50] = i*i*i;

    }

    while (scanf("%d%d%d%d%d", &a, &b, &c, &d, &e) == 5) {

        ans = 0;

        for (int i = -50; i <= 50; ++i) {

            for (int j = -50; j <= 50; ++j) {

                x = -(a * rec[i+50] + b * rec[j+50]);

                if (i != 0 && j != 0) {

                    Hash(x); 

                }

            }

        }

        for (int i = -50; i <= 50; ++i) {

        //    printf("i = %d\n", i);

            for (int j = -50; j <= 50; ++j) {

                for (int k = -50; k <= 50; ++k) {

                    if (i != 0 && j != 0 && k != 0) {

                        x = c * rec[i+50] + d * rec[j+50] + e * rec[k+50];

                        ans += find(x);

                    }

                }

            }

        }

        printf("%d\n", ans);

    }

    return 0;

}

静态：

#include <cstdio>

#include <cstring>

#include <cstdlib>

#define MOD 20003

using namespace std;



int rec[105], idx;



struct Node

{

    int x, cnt, next; 

}e[20003];



int head[20003];



void Hash(int key)

{ 

    int flag = 0, x = key;

    key = abs(key) % MOD;

    for (int i = head[key]; i != -1; i = e[i].next) {

        if (e[i].x == x) {

            flag = 1;

            ++e[i].cnt;

        }

    }

    if (!flag) {

        ++idx;

        e[idx].x = x, e[idx].cnt = 1;

        e[idx].next = head[key];

        head[key] = idx;

    }

}



int find(int key)

{

    int ans = 0, x = key;

    key = abs(key) % MOD; 

    for (int i = head[key]; i != -1; i = e[i].next) {

        if (e[i].x == x) {

            ans += e[i].cnt;

        }

    }

    return ans;

}



int main()

{

    int a, b, c, d, e, ans, x; 

    for (int i = -50; i <= 50; ++i) {

        rec[i+50] = i*i*i;

    }

    while (scanf("%d%d%d%d%d", &a, &b, &c, &d, &e) == 5) {

        memset(head, 0xff, sizeof (head));

        idx = -1;

        ans = 0;

        for (int i = -50; i <= 50; ++i) {

            for (int j = -50; j <= 50; ++j) {

                x = -(a * rec[i+50] + b * rec[j+50]);

                if (i != 0 && j != 0) {

                    Hash(x); 

                }

            }

        }

        for (int i = -50; i <= 50; ++i) {

            for (int j = -50; j <= 50; ++j) {

                for (int k = -50; k <= 50; ++k) {

                    if (i != 0 && j != 0 && k != 0) {

                        x = c * rec[i+50] + d * rec[j+50] + e * rec[k+50];

                        ans += find(x);

                    }

                }

            }

        }

        printf("%d\n", ans);

    }

    return 0;

}