UVA 11205 - The broken pedometer

最新推荐文章于 2017-11-21 15:31:00 发布

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最新推荐文章于 2017-11-21 15:31:00 发布

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原文链接：http://www.cnblogs.com/frankdj412/archive/2013/01/30/2883463.html

本文介绍了一种通过暴力解法结合哈希表来解决特定编程问题的方法。作者详细记录了实现过程中的难点及优化尝试，最终虽遭遇运行时间超限的问题，但仍为读者提供了有价值的代码实例。

暴力.完全的暴力.把每种情况都考虑进去.没办法.

这道题我还练习了一下hash table的用法。感觉这次的code写的不好看不够直观。

最后还Time Limit Exceeded.....是我的Hash不够好么？

View Code

#include <iostream>
using namespace std;

const int MAXLED = 15;
const int MAXLINE = 100;
const int MAXHASHSIZE = 10000000;
const int MAXSTATE = 1<<16;

typedef int State[MAXLED];

int head[MAXHASHSIZE], next[MAXSTATE];
State data[MAXLINE];


// Use hash table
void init_lookup_table(){
    // memset(head, -1, sizeof(head));
    // memset(next, -1, sizeof(next));
    for (int i = 0; i < MAXHASHSIZE; i++)
        head[i] = -1;
    for (int i = 0; i < MAXSTATE; i++)
        next[i] = -1;
}

int hash(State& led, int pattern, int p) {
    int num = 0;

    for (int i = 1; i <= p; i++){
        num *= 10;
        if (pattern & (1<<i)){
            num += led[i-1];
        }
    }

    return num % MAXHASHSIZE;
}

bool cmp_pattern(int s, int u, int pattern, int p) {
    for (int i = 1; i <= p; i++){
        if (pattern & (1<<i)){
            if (data[s] != data[u])
                return false;
        }
    }
    return true;
}

bool try_to_insert(int s, int pattern, int p) {
    int h = hash(data[s], pattern, p);
    int u = head[h];

    while (u != -1){
        if (!cmp_pattern(s, u, pattern, p))
            return false;
        u = next[u];
    }
    next[s] = head[h];
    head[h] = s;

    return true;
}


int main(int argc, char *argv[]){

// #ifndef ONLINE_JUDGE
//     freopen("11205.txt", "r", stdin);
// #endif

    int times;
    for (int i = 0 ; i < MAXLINE; i++)
        for (int j = 0; j < MAXLED; j++)
            data[i][j] = 0;
    cin >> times;

    while (times--){
        int p, n; // p: # of LEDs, n: # of symbols
        cin >> p >> n;

        // Input the dataset
        for (int i = 0; i < n; i++)
            for (int j = 0; j < p; j++)
                cin >> data[i][j];

        int num = 15;
        for (int i = 2; i < (1<<p); i++){
            int pattern = i, temp = i, ones = 0;
            init_lookup_table();

            for (int j = 1; j <= p; j++){
                if (pattern & (1<<j))
                    ones++;
            }

            if (ones >= num)
                continue;

            bool smaller = true;
            for (int j = 0; j < n && smaller; j++){
                smaller = try_to_insert(j, pattern, p);
                if (!smaller)
                    break;
            }
            if (smaller){
                num = ones;
            }
        }
        cout << num << endl;
    }
    return 0;
}