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package 第01期.mca_08_dp;
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// 这个问题leetcode上可以直接测
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// 链接：https://leetcode.com/problems/longest-common-subsequence/
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public class Code07_LongestCommonSubsequence {
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public static int longestCommonSubsequence1(String s1, String s2) {
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if (s1 == null || s2 == null || s1.length() == 0 || s2.length() == 0) {
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return 0;
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}
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char[] str1 = s1.toCharArray();
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char[] str2 = s2.toCharArray();
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// 尝试
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return process1(str1, str2, str1.length - 1, str2.length - 1);
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}
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public static int process1(char[] str1, char[] str2, int i, int j) {
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if (i == 0 && j == 0) {
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return str1[i] == str2[j] ? 1 : 0;
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} else if (i == 0) {
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if (str1[i] == str2[j]) {
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return 1;
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} else {
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return process1(str1, str2, i, j - 1);
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}
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} else if (j == 0) {
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if (str1[i] == str2[j]) {
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return 1;
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} else {
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return process1(str1, str2, i - 1, j);
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}
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} else { // i != 0 && j != 0
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int p1 = process1(str1, str2, i - 1, j);
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int p2 = process1(str1, str2, i, j - 1);
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int p3 = str1[i] == str2[j] ? (1 + process1(str1, str2, i - 1, j - 1)) : 0;
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return Math.max(p1, Math.max(p2, p3));
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}
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}
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public static int longestCommonSubsequence2(String s1, String s2) {
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if (s1 == null || s2 == null || s1.length() == 0 || s2.length() == 0) {
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return 0;
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}
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char[] str1 = s1.toCharArray();
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char[] str2 = s2.toCharArray();
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int N = str1.length;
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int M = str2.length;
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int[][] dp = new int[N][M];
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dp[0][0] = str1[0] == str2[0] ? 1 : 0;
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for (int j = 1; j < M; j++) {
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dp[0][j] = str1[0] == str2[j] ? 1 : dp[0][j - 1];
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}
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for (int i = 1; i < N; i++) {
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dp[i][0] = str1[i] == str2[0] ? 1 : dp[i - 1][0];
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}
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for (int i = 1; i < N; i++) {
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for (int j = 1; j < M; j++) {
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int p1 = dp[i - 1][j];
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int p2 = dp[i][j - 1];
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int p3 = str1[i] == str2[j] ? (1 + dp[i - 1][j - 1]) : 0;
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dp[i][j] = Math.max(p1, Math.max(p2, p3));
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}
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}
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return dp[N - 1][M - 1];
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}
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}
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