POJ 1018 Communication System（搜索/贪心/动归）

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搜索（TLE）：

//poj 1018//2014-6-10#include <iostream>#include <cstdio>using namespace std;const int MAX_N = 100;const int INF = 0x3f3f3f3f;int n;struct M{int b, p;} m[MAX_N][MAX_N];int num[MAX_N];double ans = -1;//force searchvoid search ( int cur , int minB, int sum ){if ( cur == n ){ans = max ( ans, 1.0 * minB / sum );return;}for ( int j = 0; j < num[cur]; j++ ){int Min = min ( minB, m[cur][j].b );search ( cur + 1, Min, sum + m[cur][j].p );}}int main(){//freopen ( "in.txt", "r", stdin );int t;scanf ( "%d", &t );while ( t-- ){ans = -1;scanf ( "%d", &n );for ( int i = 0; i < n; i++ ){scanf ( "%d", &num[i] );for ( int j = 0; j < num[i]; j++ ){scanf ( "%d%d", &m[i][j].b, &m[i][j].p );}}search ( 0, INF, 0 );printf ( "%.3f\n", ans );}return 0;}

贪心法（AC / 47MS)：

从1到Max Bandwidth枚举brandwidth，对于每个manufacturers取最小 price。

int maxb = -1;void solve(){//enmu all bandwidthfor ( int b = 1; b <= maxb; b++ ){int sum = 0;for ( int i = 0; i < n; i++ ){int Min = INF;for ( int j = 0; j < num[i]; j++ ){if(m[i][j].b >= b)Min = min ( Min, m[i][j].p );}sum += Min;}ans = max ( ans, 1.0 * b / sum );}}

动归 AC / 16MS（参照别人的= = ，可见我DP有多渣渣）：

dp[i][j] 选择第i个设备时，带宽为j的最小费用。

#include <iostream>#include <cstdio>using namespace std;const int MAX_N = 100;const int INF = 0x3f3f3f3f;int n;struct M{int b, p;} m[MAX_N][MAX_N];int num[MAX_N];int maxb = -1;int d[MAX_N][1009];void dp(){memset ( d, 0x3f, sizeof ( d ) );memset ( d, 0, sizeof ( d[0] ) );for ( int i = 1; i <= n; i++ ){for ( int j = 1; j <= num[i]; j++ ){for ( int k = 1; k <= m[i][j].b; k++ ){d[i][k] = min ( d[i][k], d[i - 1][k] + m[i][j].p );}}}double ans = 0;for ( int i = 1; i <= maxb; i++ ){ans = max ( ans, 1.0 * i / d[n][i] );}printf ( "%.3lf\n", ans );}int main(){freopen ( "in.txt", "r", stdin );int t;scanf ( "%d", &t );while ( t-- ){scanf ( "%d", &n );for ( int i = 1; i <= n; i++ ){scanf ( "%d", &num[i] );for ( int j = 1; j <= num[i]; j++ ){scanf ( "%d%d", &m[i][j].b, &m[i][j].p );maxb = max ( maxb, m[i][j].b );}}dp();}return 0;}

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