add for code

Author: houbb

src/main/java/com//houbb/leetcode/topics/editdistance/T72_minDistanceList_V1_DP.java

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+package com..houbb.leetcode.topics.editdistance;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class T72_minDistanceList_V1_DP {
+
+public static void main(String[] args) {
+T72_minDistanceList_V1_DP dp = new T72_minDistanceList_V1_DP();
+System.out.println(dp.minDistance("horse", "ros"));
+}
+
+
+public List<String> minDistance(String word1, String word2) {
+int m = word1.length();
+int n = word2.length();
+
+// DP数组，记录最小操作数
+int[][] dp = new int[m + 1][n + 1];
+// 操作类型数组，记录操作类型："" = no-op, "insert", "delete", "replace"
+String[][] operation = new String[m + 1][n + 1];
+
+// 初始化
+for (int i = 0; i <= m; i++) {
+dp[i][0] = i;
+operation[i][0] = "delete";
+}
+for (int j = 0; j <= n; j++) {
+dp[0][j] = j;
+operation[0][j] = "insert";
+}
+
+// 填充DP表和操作类型表
+for (int i = 1; i <= m; i++) {
+for (int j = 1; j <= n; j++) {
+if (word1.charAt(i - 1) == word2.charAt(j - 1)) {
+dp[i][j] = dp[i - 1][j - 1];
+operation[i][j] = ""; // 字符相等，不需要操作
+} else {
+int insert = dp[i][j - 1] + 1;
+int delete = dp[i - 1][j] + 1;
+int replace = dp[i - 1][j - 1] + 1;
+
+// 选择最小的操作
+dp[i][j] = Math.min(Math.min(insert, delete), replace);
+
+// 记录操作类型
+if (dp[i][j] == insert) {
+operation[i][j] = "insert";
+} else if (dp[i][j] == delete) {
+operation[i][j] = "delete";
+} else {
+operation[i][j] = "replace";
+}
+}
+}
+}
+
+// 回溯操作路径，生成变换过程
+List<String> result = new ArrayList<>();
+int i = m, j = n;
+StringBuilder currentWord = new StringBuilder(word1);
+
+// 回溯路径
+while (i > 0 || j > 0) {
+addNewWord(result, currentWord.toString());
+if (operation[i][j].equals("")) {
+i--;
+j--;
+} else if (operation[i][j].equals("insert")) {
+currentWord.insert(i, word2.charAt(j - 1));
+j--;
+} else if (operation[i][j].equals("delete")) {
+currentWord.deleteCharAt(i - 1);
+i--;
+} else if (operation[i][j].equals("replace")) {
+currentWord.setCharAt(i - 1, word2.charAt(j - 1));
+i--;
+j--;
+}
+}
+
+// 添加初始单词到变换过程
+addNewWord(result, currentWord.toString());
+
+// 由于回溯是从后往前的，因此需要反转结果
+// Collections.reverse(result);
+return result;
+}
+
+// 避免数据重复
+private void addNewWord(List<String> list, String word) {
+if(list.size() > 0 && word.equals(list.get(list.size()-1))) {
+return;
+}
+
+list.add(word);
+}
+
+
+}

src/main/java/com//houbb/leetcode/topics/editdistance/T72_minDistance_V1_BF.java

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+package com..houbb.leetcode.topics.editdistance;
+
+public class T72_minDistance_V1_BF {
+
+public int minDistance(String word1, String word2) {
+return helper(word1, word2, word1.length(), word2.length());
+}
+
+// 递归函数，计算word1[0..i]到word2[0..j]的最小编辑距离
+private int helper(String word1, String word2, int i, int j) {
+// 如果 word1 为空，则需要插入所有 word2 的字符
+if (i == 0) return j;
+
+// 如果 word2 为空，则需要删除所有 word1 的字符
+if (j == 0) return i;
+
+// 如果字符相等，则不需要任何操作，直接比较剩下的子串
+if (word1.charAt(i - 1) == word2.charAt(j - 1)) {
+return helper(word1, word2, i - 1, j - 1);
+}
+
+// 如果字符不相等，则考虑三种操作
+int insert = helper(word1, word2, i, j - 1); // 插入
+int delete = helper(word1, word2, i - 1, j); // 删除
+int replace = helper(word1, word2, i - 1, j - 1); // 替换
+
+// 返回三种操作中的最小值 + 1（表示进行了一次操作）
+return 1 + Math.min(Math.min(insert, delete), replace);
+}
+
+
+}

src/main/java/com//houbb/leetcode/topics/editdistance/T72_minDistance_V2_BF_memory.java

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+package com..houbb.leetcode.topics.editdistance;
+
+public class T72_minDistance_V2_BF_memory {
+
+public int minDistance(String word1, String word2) {
+int m = word1.length();
+int n = word2.length();
+Integer[][] memo = new Integer[m + 1][n + 1];
+return helper(word1, word2, m, n, memo);
+}
+
+private int helper(String word1, String word2, int i, int j, Integer[][] memo) {
+// 递归终止条件
+if (i == 0) return j; // 将空字符串转换成 word2[0..j-1]
+if (j == 0) return i; // 将 word1[0..i-1] 转换成空字符串
+
+// 如果已经计算过该子问题，直接返回结果
+if (memo[i][j] != null) return memo[i][j];
+
+// 计算当前子问题的解
+if (word1.charAt(i - 1) == word2.charAt(j - 1)) {
+memo[i][j] = helper(word1, word2, i - 1, j - 1, memo); // 字符相等，不需要任何操作
+} else {
+// 否则，考虑三种操作
+int insert = helper(word1, word2, i, j - 1, memo); // 插入
+int delete = helper(word1, word2, i - 1, j, memo); // 删除
+int replace = helper(word1, word2, i - 1, j - 1, memo); // 替换
+memo[i][j] = Math.min(Math.min(insert, delete), replace) + 1;
+}
+
+return memo[i][j];
+}
+
+
+}

src/main/java/com//houbb/leetcode/topics/editdistance/T72_minDistance_V3_DP.java

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+package com..houbb.leetcode.topics.editdistance;
+
+public class T72_minDistance_V3_DP {
+
+public int minDistance(String word1, String word2) {
+int m = word1.length();
+int n = word2.length();
+
+// 创建dp数组，dp[i][j]表示word1[0..i-1]转换为word2[0..j-1]的最小操作数
+int[][] dp = new int[m + 1][n + 1];
+
+// 初始化第一列和第一行
+for (int i = 0; i <= m; i++) {
+dp[i][0] = i; // 从word1[0..i-1]变为空字符串需要i次删除
+}
+
+for (int j = 0; j <= n; j++) {
+dp[0][j] = j; // 从空字符串变成word2[0..j-1]需要j次插入
+}
+
+// 填充dp表
+for (int i = 1; i <= m; i++) {
+for (int j = 1; j <= n; j++) {
+if (word1.charAt(i - 1) == word2.charAt(j - 1)) {
+dp[i][j] = dp[i - 1][j - 1]; // 如果字符相等，不需要任何操作
+} else {
+dp[i][j] = Math.min(Math.min(dp[i - 1][j], dp[i][j - 1]), dp[i - 1][j - 1]) + 1;
+// 三种操作：删除、插入、替换
+}
+}
+}
+
+// 最终结果是将word1完全转为word2
+return dp[m][n];
+}
+
+
+}

src/main/java/com//houbb/leetcode/topics/editdistance/T72_minDistance_V4_DP_memOpt.java

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+package com..houbb.leetcode.topics.editdistance;
+
+public class T72_minDistance_V4_DP_memOpt {
+
+public int minDistance(String word1, String word2) {
+int m = word1.length();
+int n = word2.length();
+
+// 用两个一维数组代替二维数组
+int[] prev = new int[n + 1];
+int[] curr = new int[n + 1];
+
+// 初始化第一行
+for (int j = 0; j <= n; j++) {
+prev[j] = j;
+}
+
+// 填充动态规划表
+for (int i = 1; i <= m; i++) {
+curr[0] = i; // 第i行的第0列，表示将word1[0..i-1]转换为空字符串，需要i次删除
+for (int j = 1; j <= n; j++) {
+if (word1.charAt(i - 1) == word2.charAt(j - 1)) {
+curr[j] = prev[j - 1]; // 字符相等，无需操作
+} else {
+curr[j] = Math.min(Math.min(prev[j], curr[j - 1]), prev[j - 1]) + 1; // 三种操作的最小值
+}
+}
+// 更新prev和curr
+int[] temp = prev;
+prev = curr;
+curr = temp;
+}
+
+return prev[n]; // 返回最后的结果
+}
+
+
+}

src/main/java/com//houbb/leetcode/topics/package-info.java

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+package com..houbb.leetcode.topics;