2025-01-25 KMP算法-查找字符串问题

src/dataANDcalc/java/algorithm/KMP.java

@@ -0,0 +1,124 @@
+package algorithm;
+
+import java.util.ArrayList;
+
+public class KMP {
+
+    private String searchStr;
+
+    private String targetStr;
+
+    private String[] strMatchs;
+
+    private int[] postMatchs;
+
+    private ArrayList<String> prefixs;
+
+    private ArrayList<String> suffixs;
+
+    public KMP(String searchStr, String targetStr){
+        this.searchStr = searchStr;
+        this.targetStr = targetStr;
+        prefixs = new ArrayList<>();
+        suffixs = new ArrayList<>();
+        strMatchs = new String[targetStr.length()];
+        postMatchs = new int[targetStr.length()];
+        for(int i = 0; i<targetStr.length(); i++){
+            strMatchs[i] = targetStr.substring(i, i+1);
+        }
+    }
+
+    private void prefixSuffixMatchs(int length){
+        for(int i = 1; i<length; i++){
+            String prefix = targetStr.substring(0, i);
+            prefixs.add(prefix);
+            String suffix = targetStr.substring(length - i, length);
+            suffixs.add(suffix);
+        }
+        for(String prefix : prefixs){
+            for(String suffix : suffixs){
+                if(prefix.equals(suffix)){
+                    postMatchs[length - 1] = prefix.length();
+                }
+            }
+        }
+        prefixs.clear();
+        suffixs.clear();
+    }
+
+    private void makeMatchs(){
+        for(int i = 7; i > 0; i--){
+            prefixSuffixMatchs(i);
+        }
+    }
+
+    private void makeMatchsOp(){
+        for(int i = 1, j = 0; i < targetStr.length(); i++){
+            //当targetStr.charAt(i) != targetStr(j) , 需要从postMatchs[j - 1]获取新的j ， 直到发现有相等的才退出
+            while(j > 0 && targetStr.charAt(i) != targetStr.charAt(j)){
+                // 为什么获取新的j是postMatchs[j-1]呢？？
+                j = postMatchs[j - 1];
+            }
+            if(targetStr.charAt(i) == targetStr.charAt(j)){
+                j++;
+            }
+            postMatchs[i] = j;
+        }
+    }
+
+    private int kmpSearch(){
+        int index = 0;
+        int j = 0;
+        while(index < searchStr.length()){
+            String searchChar = searchStr.substring(index, index+1);
+            String targetChar = strMatchs[j];
+            if (!searchChar.equals(targetChar)){
+                if (j == 0){
+                    index ++ ;
+                } else {
+                    int suffixPost = j  - postMatchs[j - 1];
+                    index = index + suffixPost;
+                    j = 0;
+                }
+            }else {
+                if (j == strMatchs.length - 1){
+                    return index - j;
+                }
+                index ++;
+                j ++;
+            }
+        }
+        return -1;
+    }
+
+    private void show(){
+        System.out.println("前缀表");
+        for(String prefix : prefixs){
+            System.out.print(prefix + " ");
+        }
+        System.out.println();
+        System.out.println("后缀表");
+        for(String suffix : suffixs){
+            System.out.print(suffix + " ");
+        }
+        System.out.println();
+        System.out.println("字符串表:");
+        for(String str : strMatchs){
+            System.out.print(str + " ");
+        }
+        System.out.println();
+        System.out.println("部分匹配表:");
+        for(int post : postMatchs){
+            System.out.print(post + " ");
+        }
+    }
+
+    public static void main(String[] args) {
+        String searchStr = "BBC ABCDAB ABCDABCDABDE";
+        String targetStr = "ABCDABD";
+        KMP kmp = new KMP(searchStr, targetStr);
+        kmp.makeMatchs();
+        kmp.show();
+        System.out.println("找到匹配的字符串位置:"+kmp.kmpSearch());
+    }
+}