一些貪心算法題

1.獨木舟問題

代碼如下：

#include <bits/stdc++.h>
using namespace std;
int a[10010];
int main()
{
	int n, m;
	
	scanf( "%d%d", &n, &m);
	for ( int i = 0; i < n; i++){
		scanf( "%d", &a[i]);
	}
	sort( a, a + n);
	int x = 0, y = n - 1, s = 0;
	while ( y >= x){
		if ( a[y] + a[x] <= m)
		<span style="white-space:pre">	</span>x++;
		y--;
		s++; 
	}
	printf( "%d\n", s);
}

2.活動安排（最大活動數）

代碼如下：

#include <bits/stdc++.h>
using namespace std;
int s[10010], e[10010];
int main()
{
	int n;
	
	scanf( "%d", &n);
	for ( int i = 0; i < n; i++){
		scanf( "%d%d", &s[i], &e[i]);
	}
	for ( int i = 0; i < n - 1; i++){
		int k = i;
		for ( int j = i + 1; j < n; j++){
			if ( e[j] < e[k]){
				k = j;
			}
		}
		if ( k != i){
			swap( s[i], s[k]);
			swap( e[i], e[k]);
		}
	}
	int x = e[0], t = 1;
	for ( int i = 1; i < n; i++){
		if ( s[i] >= x){
			x = e[i];
			t++;
		}
	}
	printf( "%d\n", t);
	return 0;
}

3.活動安排（最多需要的教室數）

代碼如下：

#include <bits/stdc++.h>
using namespace std;
int s[10010], e[10010];
int main()
{
	int n;
	
	scanf( "%d", &n);
	for ( int i = 0; i < n; i++){
		scanf( "%d%d", &s[i], &e[i]);
	}
	for ( int i = 0; i < n - 1; i++){
		int k = i;
		for ( int j = i + 1; j < n; j++){
			if ( s[j] < s[k]){
				k = j;
			}
		}
		if ( k != i){
			swap( s[i], s[k]);
			swap( e[i], e[k]);
		}
	}
	int max = 0;
	for ( int i = 1; i < n; i++){
		int t = 0;
		for ( int j = i - 1; j >= 0; j--){
			if ( e[j] > s[i])
			t++;
		}
		if ( t > max)
		max = t;
	}
	printf( "%d\n", max + 1);
	return 0;
}

4.fatmouse's trade

代碼如下：

#include <cstdio>
#include <algorithm>
using namespace std;
int a[1010], b[1010];
double c[1010];
int main()
{
	int n, m, x, y;
	
	while ( scanf( "%d%d", &m, &n) == 2 && ( n != -1 || m != -1)){
		int j = 0;
		double s = 0;
		for ( int i = 0; i < n; i++){
			scanf( "%d%d", &x, &y);
			if ( y == 0){
				s += x;
			}
			else{
				a[j] = x;
				b[j] = y;
				c[j] = 1.0 * x / y;
				j++;
			}
		}
		int z = j;
		for ( int i = 0; i < z - 1; i++){
			int k = i;
			for ( int j = i + 1; j < z; j++){
				if ( c[j] > c[k])
				k = j;
			}
			if ( k != i){
				swap( c[i], c[k]);
				swap( a[i], a[k]);
				swap( b[i], b[k]);
			}
		}
		int i = 0;
		while ( m >= b[i] && i < z){
			m = m - b[i];
			s += a[i];
			i++;
		}
		if ( i < z){
			s += m * c[i];
		}
		printf( "%.3lf\n", s);
	} 
	return 0;
}