贪心算法求解背包问题

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package chapter02;

import java.util.Arrays;
import java.util.LinkedList;

public class ActivitySelection {
private int[] start; // 开始时间
private int[] finish; // 结束时间

public ActivitySelection(int[] s, int[] f) {
assert s.length == f.length;

start = s;
finish = f;
}

public ActivitySelection(int[] s, int[] f, boolean sort) {
assert s.length == f.length;
if (!sort) {
// 按结束时间进行插入排序
for (int i = 1; i < s.length; i++) {
for (int j = i; j > 0 && f[j] < f[j-1]; j--) {
swap(s, j, j-1);
swap(f, j, j-1);
}
}
}

start = s;
finish = f;
}

private void swap(int[] a, int i, int j) {
int temp = a[i]; a[i] = a[j]; a[j] = temp;
}

public int[] recurisveSelect() {
LinkedList<Integer> activities = new LinkedList<Integer>();
recursiveSelect(activities, -1, start.length);

return toIntArray(activities);
}

private int[] toIntArray(LinkedList<Integer> activities) {
int[] result = new int[activities.size()];
int i = 0;
for (int activity : activities) {
result[i++] = activity;
}
return result;
}

private void recursiveSelect(LinkedList<Integer> activities, int i, int j) {
int m = i + 1;
while ((i >= 0 && m < j && start[m] < finish[i]) || i >= start.length) {
m++;
}
if (m < j) {
activities.add(m);
recursiveSelect(activities, m, j);
}
}

public int[] select() {
LinkedList<Integer> activities = new LinkedList<Integer>();
activities.add(0); // add first activity

int i = 0;
for (int m = 1; m < start.length; m++) {
if (start[m] >= finish[i]) {
activities.add(m);
i = m;
}
}
return toIntArray(activities);
}

public static void main(String[] args) {
int[] s = new int[] {1, 3, 0, 5, 3, 5, 6, 8, 8, 2, 12};
int[] f = new int[] {4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14};

ActivitySelection as = new ActivitySelection(s, f);
int[] acts = as.recurisveSelect();
System.out.println("recursively select activites: " + Arrays.toString(acts));

acts = as.select();
System.out.println("\nselect activites: " + Arrays.toString(acts));

s = new int[] {5, 1, 3, 8, 0, 3, 5, 6, 8, 2, 12};
f = new int[] {7, 4, 5, 11, 6, 8, 9, 10, 12, 13, 14};
as = new ActivitySelection(s, f, false);
acts = as.recurisveSelect();
System.out.println("\nrecursively select activites: " + Arrays.toString(acts));

acts = as.select();
System.out.println("\n");
System.out.println("select activites: " + Arrays.toString(acts));
}
}