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92 lines
2.0 KiB
92 lines
2.0 KiB
package class20;
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public class Code04_PalindromeWays {
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public static int ways1(String str) {
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if (str == null || str.length() == 0) {
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return 0;
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}
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char[] s = str.toCharArray();
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char[] path = new char[s.length];
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return process(str.toCharArray(), 0, path, 0);
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}
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public static int process(char[] s, int si, char[] path, int pi) {
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if (si == s.length) {
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return isP(path, pi) ? 1 : 0;
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}
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int ans = process(s, si + 1, path, pi);
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path[pi] = s[si];
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ans += process(s, si + 1, path, pi + 1);
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return ans;
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}
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public static boolean isP(char[] path, int pi) {
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if (pi == 0) {
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return false;
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}
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int L = 0;
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int R = pi - 1;
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while (L < R) {
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if (path[L++] != path[R--]) {
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return false;
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}
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}
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return true;
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}
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public static int ways2(String str) {
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if (str == null || str.length() == 0) {
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return 0;
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}
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char[] s = str.toCharArray();
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int n = s.length;
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int[][] dp = new int[n][n];
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for (int i = 0; i < n; i++) {
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dp[i][i] = 1;
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}
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for (int i = 0; i < n - 1; i++) {
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dp[i][i + 1] = s[i] == s[i + 1] ? 3 : 2;
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}
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for (int L = n - 3; L >= 0; L--) {
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for (int R = L + 2; R < n; R++) {
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dp[L][R] = dp[L + 1][R] + dp[L][R - 1] - dp[L + 1][R - 1];
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if (s[L] == s[R]) {
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dp[L][R] += dp[L + 1][R - 1] + 1;
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}
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}
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}
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return dp[0][n - 1];
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}
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public static String randomString(int len, int types) {
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char[] str = new char[len];
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for (int i = 0; i < str.length; i++) {
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str[i] = (char) ('a' + (int) (Math.random() * types));
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}
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return String.valueOf(str);
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}
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public static void main(String[] args) {
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int N = 10;
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int types = 5;
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int testTimes = 100000;
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System.out.println("测试开始");
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for (int i = 0; i < testTimes; i++) {
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int len = (int) (Math.random() * N);
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String str = randomString(len, types);
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int ans1 = ways1(str);
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int ans2 = ways2(str);
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if (ans1 != ans2) {
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System.out.println(str);
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System.out.println(ans1);
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System.out.println(ans2);
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System.out.println("Oops!");
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break;
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}
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}
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System.out.println("测试结束");
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}
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}
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