poj1163 遞迴或dp

遞迴的版本：很可惜tle了。

package p1163;import java.io.File;import java.io.FileNotFoundException;import java.util.Scanner;public class Main {static int count = 105;static int d[][] = new int[count][count];static int n;public static void main(String[] args) throws FileNotFoundException {//File f = new File("c:\\data.txt");//Scanner cin = new Scanner(f); Scanner cin = new Scanner(System.in);n = cin.nextInt();for (int i = 1; i <= n; i++) {for (int j = 1; j <= i; j++) {d[i][j] = cin.nextInt();}}System.out.println(func(1, 1));}// i行，j列，j<=istatic int func(int i, int j) {int max = 0;if (i < n) {max = d[i][j] + max(func(i + 1, j), func(i + 1, j + 1));// 往下，往右} else {max = d[i][j];}return max;}static int max(int a, int b) {return a > b ? a : b;}}

想了一下，tle的原因主要是遞迴是從上往下計算的。那麼用動規呢，從下往上計算。

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動規的版本：

import java.io.File;import java.io.FileNotFoundException;import java.util.Scanner;public class Main {static int count = 105;static int d[][] = new int[count][count];static int res[][] = new int[count][count];//使用res儲存已經計算出來的資料static int n;public static void main(String[] args) throws FileNotFoundException {//File f = new File("c:\\data.txt");//Scanner cin = new Scanner(f); Scanner cin = new Scanner(System.in);n = cin.nextInt();for (int i = 1; i <= n; i++) {for (int j = 1; j <= i; j++) {d[i][j] = cin.nextInt();}}for (int i = 1; i <= n; i++) {res[n][i] = d[n][i];}// 從下往上動規for (int i = n; i >= 1; i--) {for (int j = 0; j <= i; j++) {res[i][j] = d[i][j] + max(res[i + 1][j], res[i + 1][j + 1]);}}System.out.println(res[1][1]);//最後，res數組的頂層的那個元素就是要求的最大值}static int max(int a, int b) {return a > b ? a : b;}}

其實動規跟上面的遞迴版本，差不是很多。都是從底層計算，然後向上層累加。只是遞迴版本的應該是需要遞迴很多次，所以算上遞迴返回的時間，就tle了吧。