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package class39;
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public class Code02_SnacksWays {
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public static int ways1(int[] arr, int w) {
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// arr[0...]
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return process(arr, 0, w);
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}
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// 从左往右的经典模型
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// 还剩的容量是rest，arr[index...]自由选择，
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// 返回选择方案
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// index ： 0～N
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// rest : 0~w
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public static int process(int[] arr, int index, int rest) {
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if (rest < 0) { // 没有容量了
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// -1 无方案的意思
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return -1;
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}
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// rest>=0,
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if (index == arr.length) { // 无零食可选
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return 1;
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}
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// rest >=0
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// 有零食index
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// index号零食，要 or 不要
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// index, rest
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// (index+1, rest)
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// (index+1, rest-arr[i])
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int next1 = process(arr, index + 1, rest); // 不要
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int next2 = process(arr, index + 1, rest - arr[index]); // 要
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return next1 + (next2 == -1 ? 0 : next2);
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}
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public static int ways2(int[] arr, int w) {
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int N = arr.length;
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int[][] dp = new int[N + 1][w + 1];
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for (int j = 0; j <= w; j++) {
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dp[N][j] = 1;
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}
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for (int i = N - 1; i >= 0; i--) {
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for (int j = 0; j <= w; j++) {
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dp[i][j] = dp[i + 1][j] + ((j - arr[i] >= 0) ? dp[i + 1][j - arr[i]] : 0);
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}
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}
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return dp[0][w];
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}
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public static int ways3(int[] arr, int w) {
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int N = arr.length;
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int[][] dp = new int[N][w + 1];
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for (int i = 0; i < N; i++) {
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dp[i][0] = 1;
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}
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if (arr[0] <= w) {
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dp[0][arr[0]] = 1;
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}
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for (int i = 1; i < N; i++) {
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for (int j = 1; j <= w; j++) {
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dp[i][j] = dp[i - 1][j] + ((j - arr[i]) >= 0 ? dp[i - 1][j - arr[i]] : 0);
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}
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}
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int ans = 0;
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for (int j = 0; j <= w; j++) {
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ans += dp[N - 1][j];
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}
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return ans;
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}
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public static void main(String[] args) {
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int[] arr = { 4, 3, 2, 9 };
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int w = 8;
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System.out.println(ways1(arr, w));
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System.out.println(ways2(arr, w));
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System.out.println(ways3(arr, w));
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}
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}
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