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package class11_17;
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public class Code07_Knapsack {
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public static int getMaxValue(int[] w, int[] v, int bag) {
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return process(w, v, 0, 0, bag);
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}
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// 不变 ： w[] v[] bag
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// index... 最大价值
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// 0..index-1上做了货物的选择，使得你已经达到的重量是多少alreadyW
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// 如果返回-1，认为没有方案
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// 如果不返回-1，认为返回的值是真实价值
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public static int process(int[] w, int[] v, int index, int alreadyW, int bag) {
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if (alreadyW > bag) {
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return -1;
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}
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// 重量没超
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if (index == w.length) {
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return 0;
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}
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int p1 = process(w, v, index + 1, alreadyW, bag);
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int p2next = process(w, v, index + 1, alreadyW + w[index], bag);
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int p2 = -1;
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if (p2next != -1) {
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p2 = v[index] + p2next;
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}
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return Math.max(p1, p2);
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}
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public static int maxValue(int[] w, int[] v, int bag) {
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return process(w, v, 0, bag);
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}
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// 只剩下rest的空间了，
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// index...货物自由选择，但是剩余空间不要小于0
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// 返回 index...货物能够获得的最大价值
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public static int process(int[] w, int[] v, int index, int rest) {
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if (rest < 0) { // base case 1
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return -1;
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}
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// rest >=0
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if (index == w.length) { // base case 2
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return 0;
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}
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// 有货也有空间
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int p1 = process(w, v, index + 1, rest);
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int p2 = -1;
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int p2Next = process(w, v, index + 1, rest - w[index]);
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if(p2Next!=-1) {
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p2 = v[index] + p2Next;
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}
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return Math.max(p1, p2);
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}
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public static int dpWay(int[] w, int[] v, int bag) {
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int N = w.length;
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int[][] dp = new int[N + 1][bag + 1];
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for (int index = N - 1; index >= 0; index--) {
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for (int rest = 1; rest <= bag; rest++) {
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dp[index][rest] = dp[index + 1][rest];
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if (rest >= w[index]) {
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dp[index][rest] = Math.max(dp[index][rest], v[index] + dp[index + 1][rest - w[index]]);
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}
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}
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}
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return dp[0][bag];
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}
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public static void main(String[] args) {
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int[] weights = { 3, 2, 4, 7 };
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int[] values = { 5, 6, 3, 19 };
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int bag = 11;
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System.out.println(maxValue(weights, values, bag));
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System.out.println(dpWay(weights, values, bag));
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}
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}
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