java贪心算法背包问题

背包问题是一个经典的动态规划问题，但也可以使用贪心算法来解决。具体来说，可以按照物品的单位重量价值进行排序，然后依次将单位重量价值最高的物品放入背包中，直到背包无法再放入为止。

Java代码实现如下：

public class KnapsackProblem {
    public static void main(String[] args) {
        int[] weights = {2, 3, 4, 5};
        int[] values = {3, 4, 5, 6};
        int capacity = 8;
        double maxValue = knapsack(weights, values, capacity);
        System.out.println("Max value: " + maxValue);
    }

    public static double knapsack(int[] weights, int[] values, int capacity) {
        int n = weights.length;
        double[] unitValues = new double[n];
        for (int i = 0; i < n; i++) {
            unitValues[i] = (double) values[i] / weights[i];
        }
        // 按照单位重量价值排序
        for (int i = 0; i < n - 1; i++) {
            for (int j = i + 1; j < n; j++) {
                if (unitValues[i] < unitValues[j]) {
                    swap(unitValues, i, j);
                    swap(weights, i, j);
                    swap(values, i, j);
                }
            }
        }
        // 贪心选择物品
        double maxValue = 0;
        for (int i = 0; i < n && capacity > 0; i++) {
            if (weights[i] <= capacity) {
                maxValue += values[i];
                capacity -= weights[i];
            } else {
                maxValue += unitValues[i] * capacity;
                capacity = 0;
            }
        }
        return maxValue;
    }

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

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