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            oyjpArt ACM/ICPC算法程序設(shè)計空間

            // I am new in programming, welcome to my blog
            I am oyjpart(alpc12, 四城)
            posts - 224, comments - 694, trackbacks - 0, articles - 6

            基本參數(shù)搜索

            Posted on 2008-06-03 15:45 oyjpart 閱讀(3129) 評論(14)  編輯 收藏 引用 所屬分類: ACM/ICPC或其他比賽

            上次百度之星第三題竟然不會做,很是慚愧啊,腦袋生銹了。

            后來從HUST上面找了道類似的題目,AC了。


            The perfect hamilton path

            Time Limit: 5 Sec  Memory Limit: 128 MB
            Submissions: 72  Solved: 16

            Description

            There are N(2 <= N <= 13) cities and M bidirectional roads among the cities. There exist at most one road between any pair of the cities. Along every road, there are G pretty girls and B pretty boys(1 <= G,B <= 1000).
            You want to visit every city exactly once, and you can start from any city you want to. The degree of satisfaction is the ratio of the number of the pretty girls to the number of the pretty boys. You want to know the highest degree of satisfation.

            Input

            There are multiply test cases.
            First line: two integers N, M;
            The following M lines: every line with four integers i, j, G, B, response that there is a road between i and j with G and B.

            Output

            The highest degree of the satisfation, rounded to the third place after the decimal point.

            Sample Input

            3 3
            1 2 5 3
            2 3 7 4
            3 1 13 11

            Sample Output

            1.714

            HINT

            Source

            dupeng


            題目的意思是找到一個sigma(G)/sigma(B)最大的hamilton回路。
            典型的參數(shù)搜索。二分或者迭代答案就可以了。

            Solution:

            #include <stdio.h>
            #include 
            <queue>
            #include 
            <cmath>
            using namespace std;

            const double EPS = 1e-4;
            const int N = 15;
            const int M = N * N;

            #define Max(a, b) (a
            >b?a:b)

            inline 
            int dblcmp(double a, double b) {
                
            if(fabs(a-b) < EPS) return 0;
                
            return a < b ? -1 : 1;
            }

            struct Node 
            {
                
            int x, mask;
                
            double s;
                Node() {}
                Node(
            int mm, int xx, double ss) {
                    x 
            = xx;
                    mask 
            = mm;
                    s 
            = ss;
                }
            };

            int n, m;

            double adj[N][N];
            int X[M], Y[M], G[M], B[M];

            double dp[1<<N][N];

            double go(double ans) {
                
            int i, j;
                
            for(i = 0; i < n; ++i) {
                    adj[i][i] 
            = 0;
                    
            for(j = i+1; j < n; ++j) {
                        adj[i][j] 
            = adj[j][i] = -10e300;
                    }
                }
                
            for(i = 0; i < m; ++i) {
                    adj[X[i]
            -1][Y[i]-1= G[i]-ans * B[i];
                    adj[Y[i]
            -1][X[i]-1= adj[X[i]-1][Y[i]-1];
                }

                
            for(i = 0; i < (1<<n); ++i) {
                    
            for(j = 0; j < n; ++j)
                        dp[i][j] 
            = -10e100;
                }
                queue
            <Node> Q;
                
            for(i = 0; i < n; ++i) {
                    Q.push(Node(
            1<<i, i, 0.0));
                    dp[
            1<<i][i] = 0;
                }
                
            while(Q.size()) {
                    
            int f = Q.front().mask, x = Q.front().x;
                    
            double s = Q.front().s;
                    
            double& d = dp[f][x];
                    Q.pop();
                    
            if(s < d) continue;
                    
            for(i = 0; i < n; ++i) if((f&(1<<i)) == 0) {
                        
            if(dp[f|1<<i][i] < s + adj[x][i]) {
                            dp[f
            |1<<i][i] = s + adj[x][i];
                            Q.push(Node(f
            |1<<i, i, s + adj[x][i]));
                        }
                    }
                }

                
            double max = -10e100;
                
            for(i = 0; i < n; ++i) {
                    max 
            = Max(max, dp[(1<<n)-1][i]);
                }
                
            return max;
            }

            int main()
            {
                
            // freopen("t.in", "r", stdin);

                
            int i;
                
            double ans;
                
            while(scanf("%d %d"&n, &m) != EOF) {
                    
            double min = 2000, max = 0;
                    
            for(i = 0; i < m; ++i) {
                        scanf(
            "%d %d %d %d"&X[i], &Y[i], &G[i], &B[i]);
                        
            if(B[i] < min) min = B[i];
                        
            if(G[i] > max) max = G[i];
                    }
                    
            double lo = 0, hi = max/min;
                    
            int ok = 0;
                    
            for(i = 0; ; ++i) {
                        
            double mid = lo + (hi-lo)/2;
                        
            if(dblcmp((ans=go(mid)), 0.0> 0) {
                            lo 
            = mid;
                        } 
            else if(dblcmp(ans, 0.0== 0) {
                            printf(
            "%.3lf\n", mid);
                            ok 
            = 1;
                            
            break;
                        } 
            else {
                            hi 
            = mid;
                        }
                    }

                    
            if(!ok) { int a = 0; a = 1/a; }
                }

                
            return 0;
            }

             


            Feedback

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-06-04 13:43 by w
            你好,這個程序我看不懂……能講一下思路嗎?

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-06-04 14:56 by oyjpart
            你可以參考《算法藝術(shù)與信息學競賽》303-304頁
            3.地震--最有比率生成樹 一節(jié)的解答
            和這個非常類似

            就是2分枚舉那個答案,然后將除的表達式的權(quán) 轉(zhuǎn)化成+-*表達式的權(quán),再這個基礎(chǔ)上求目標函數(shù)。 如果目標函數(shù) != 0,則枚舉的答案應(yīng)該向使目標函數(shù)更接近0的方向取值,

            go函數(shù)實際求的就是最大權(quán)的hamilton回路。用的是基本的壓縮狀態(tài)廣搜。

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-06-04 15:02 by Surfing
            我的解法

            #include <stdio.h>

            #define N 13

            typedef struct _T_AdjNode
            {
            int nBoys;
            int nGirls;
            double dRatio;
            }TAdjNode;

            TAdjNode g_AdjNode[N][N];
            int g_Path[2][N];
            int g_PathIndex[2] = {0};
            double g_dRatio[2] = {0.0};
            int nCities, nRoads;

            int FindNextNode(int nPathIndex, int nLine)
            {
            double dRatio = 0;
            int nNode = 0;
            int i = 0;
            int j = 0;
            bool bExist = false;

            for (j = 0; j < nCities; j++)
            {
            for (i = 0; i < g_PathIndex[nPathIndex]; i++)
            {
            if (j == g_Path[nPathIndex][i])
            {
            bExist = true;
            break;
            }
            }
            if (bExist)
            {
            bExist = false;
            continue;
            }
            if (g_AdjNode[nLine][j].dRatio > dRatio)
            {
            dRatio = g_AdjNode[nLine][j].dRatio;
            nNode = j;
            }
            }

            return nNode;
            }

            int FindPath(int nPathIndex, int nNode)
            {
            int nNextNode = 0;
            static int nBoys = 0, nGirls = 0;

            g_Path[nPathIndex][g_PathIndex[nPathIndex]] = nNode;
            g_PathIndex[nPathIndex]++;
            if (g_PathIndex[nPathIndex] >= nCities)
            {
            g_dRatio[nPathIndex] = (double)nGirls / nBoys;
            return 0;
            }

            nNextNode = FindNextNode(nPathIndex, nNode);
            nBoys += g_AdjNode[nNode][nNextNode].nBoys;
            nGirls += g_AdjNode[nNode][nNextNode].nGirls;
            FindPath(nPathIndex, nNextNode);

            return 0;
            }

            int main()
            {
            int i,j,nGirls,nBoys;
            char q = '0';
            int nPathIndex = 0;

            nCities = nRoads = 0;
            i = j = nGirls = nBoys = 0;

            printf("Input the number of cities and roads:\n");
            scanf("%d %d", &nCities, &nRoads);

            if (nCities < 1 || nRoads < 1)
            {
            return 1;
            }

            do
            {
            printf("Input the road index and the number of girls and boys sequentially : "
            "from to girls boys\n");
            scanf("%d %d %d %d", &i, &j, &nGirls, &nBoys);
            getchar();

            g_AdjNode[i - 1][j - 1].nBoys = nBoys;
            g_AdjNode[i - 1][j - 1].nGirls = nGirls;
            g_AdjNode[i - 1][j - 1].dRatio = (double)nGirls / nBoys;
            g_AdjNode[j - 1][i - 1].nBoys = nBoys;
            g_AdjNode[j - 1][i - 1].nGirls = nGirls;
            g_AdjNode[j - 1][i - 1].dRatio = g_AdjNode[i - 1][j - 1].dRatio;

            printf("Input finished?(y/n)");
            scanf("%c", &q);
            getchar();
            } while ('y' != q);

            //process here
            nPathIndex = 0;
            for (i = 0; i < nCities; i++)
            {
            FindPath(nPathIndex, 0);
            nPathIndex = g_dRatio[0] <= g_dRatio[1] ? 0 : 1;
            g_PathIndex[nPathIndex] = 0;
            }

            //output the result
            nPathIndex = g_dRatio[0] >= g_dRatio[1] ? 0 : 1;
            printf("The max ratio is %.3lf\n", g_dRatio[nPathIndex]);\
            printf("The best path : \n");
            for (i = 0; i < nCities; i++)
            {
            printf("%d\t", g_Path[nPathIndex][i]);
            }
            printf("\n");

            return 0;
            }

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-06-04 15:10 by Surfing
            一點小問題,更正一下

            if (g_PathIndex[nPathIndex] >= nCities)
            {
            g_dRatio[nPathIndex] = (double)nGirls / nBoys;
            nGirls = nBoys = 0;
            return 0;
            }

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-06-04 17:13 by oyjpart
            @Surfing
            嘿嘿,謝謝分享

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-06-05 22:27 by w
            多謝,受教了

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-06-05 23:07 by oyjpart
            不謝

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-06-09 23:54 by richardxx
            我做了百度那題,但比賽完才想起我貼的那個模版有點問題,最后果然只有4.5分,和沒做沒區(qū)別~~

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-06-10 12:03 by oyjpart
            @richardxx
            呵呵 進復(fù)賽了就可以了不 看我們這種初賽就被水掉的菜菜。。

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-06-10 20:01 by 小Young
            跟著大牛漲經(jīng)驗值!

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-06-10 20:34 by oyjpart
            汗。。。
            您謙虛了。。。

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-06-11 19:12 by 小Young
            請問這題你用隊列有什么用途啊?
            這題不用隊列也可以啊.

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-06-11 22:19 by oyjpart
            @ 小Young
            就是廣搜用的隊列
            不用隊列你的意思是深搜么?

            # re: 基本參數(shù)搜索  回復(fù)  更多評論   

            2008-07-26 06:09 by lengbufang
            看看!!!
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