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GeezerVison is showing github.com — Java/DynamicProgramming/RegexMatching.java at master · AmaranthLIS/Java

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package DynamicProgramming;
/**
* Given a text and wildcard pattern implement a wildcard pattern matching
* algorithm that finds if wildcard is matched with text. The matching should
* cover the entire text
* ?-> matches single characters
* *-> match the sequence of characters
**/
/**
* For calculation of Time and Space Complexity. Let N be length of src and M be length of pat
**/
public class RegexMatching {
// Method 1: Using Recursion
// Time Complexity=0(2^(N+M)) Space Complexity=Recursion Extra Space
static boolean regexRecursion(String src, String pat) {
if (src.length() == 0 && pat.length() == 0) {
return true;
}
if (src.length() != 0 && pat.length() == 0) {
return false;
}
if (src.length() == 0 && pat.length() != 0) {
for (int i = 0; i < pat.length(); i++) {
if (pat.charAt(i) != '*') {
return false;
}
}
return true;
}
char chs = src.charAt(0);
char chp = pat.charAt(0);
String ros = src.substring(1);
String rop = pat.substring(1);
boolean ans;
if (chs == chp || chp == '?') {
ans = regexRecursion(ros, rop);
} else if (chp == '*') {
boolean blank = regexRecursion(src, rop);
boolean multiple = regexRecursion(ros, pat);
ans = blank || multiple;
} else {
ans = false;
}
return ans;
}
// Method 2: Using Recursion and breaking string using virtual index
// Time Complexity=0(2^(N+M)) Space Complexity=Recursion Extra Space
static boolean regexRecursion(String src, String pat, int svidx, int pvidx) {
if (src.length() == svidx && pat.length() == pvidx) {
return true;
}
if (src.length() != svidx && pat.length() == pvidx) {
return false;
}
if (src.length() == svidx && pat.length() != pvidx) {
for (int i = pvidx; i < pat.length(); i++) {
if (pat.charAt(i) != '*') {
return false;
}
}
return true;
}
char chs = src.charAt(svidx);
char chp = pat.charAt(pvidx);
boolean ans;
if (chs == chp || chp == '?') {
ans = regexRecursion(src, pat, svidx + 1, pvidx + 1);
} else if (chp == '*') {
boolean blank = regexRecursion(src, pat, svidx, pvidx + 1);
boolean multiple = regexRecursion(src, pat, svidx + 1, pvidx);
ans = blank || multiple;
} else {
ans = false;
}
return ans;
}
// Method 3: Top-Down DP(Memoization)
// Time Complexity=0(N*M) Space Complexity=0(N*M)+Recursion Extra Space
static boolean regexRecursion(String src, String pat, int svidx, int pvidx, int[][] strg) {
if (src.length() == svidx && pat.length() == pvidx) {
return true;
}
if (src.length() != svidx && pat.length() == pvidx) {
return false;
}
if (src.length() == svidx && pat.length() != pvidx) {
for (int i = pvidx; i < pat.length(); i++) {
if (pat.charAt(i) != '*') {
return false;
}
}
return true;
}
if (strg[svidx][pvidx] != 0) {
return strg[svidx][pvidx] == 1 ? false : true;
}
char chs = src.charAt(svidx);
char chp = pat.charAt(pvidx);
boolean ans;
if (chs == chp || chp == '?') {
ans = regexRecursion(src, pat, svidx + 1, pvidx + 1, strg);
} else if (chp == '*') {
boolean blank = regexRecursion(src, pat, svidx, pvidx + 1, strg);
boolean multiple = regexRecursion(src, pat, svidx + 1, pvidx, strg);
ans = blank || multiple;
} else {
ans = false;
}
strg[svidx][pvidx] = ans == false ? 1 : 2;
return ans;
}
// Method 4: Bottom-Up DP(Tabulation)
// Time Complexity=0(N*M) Space Complexity=0(N*M)
static boolean regexBU(String src, String pat) {
boolean strg[][] = new boolean[src.length() + 1][pat.length() + 1];
strg[src.length()][pat.length()] = true;
for (int row = src.length(); row >= 0; row--) {
for (int col = pat.length() - 1; col >= 0; col--) {
if (row == src.length()) {
if (pat.charAt(col) == '*') {
strg[row][col] = strg[row][col + 1];
} else {
strg[row][col] = false;
}
} else {
char chs = src.charAt(row);
char chp = pat.charAt(col);
boolean ans;
if (chs == chp || chp == '?') {
ans = strg[row + 1][col + 1];
} else if (chp == '*') {
boolean blank = strg[row][col + 1];
boolean multiple = strg[row + 1][col];
ans = blank || multiple;
} else {
ans = false;
}
strg[row][col] = ans;
}
}
}
return strg[0][0];
}
public static void main(String[] args) {
String src = "aa";
String pat = "*";
System.out.println("Method 1: "+regexRecursion(src, pat));
System.out.println("Method 2: "+regexRecursion(src, pat, 0, 0));
System.out.println("Method 3: "+regexRecursion(src, pat, 0, 0, new int[src.length()][pat.length()]));
System.out.println("Method 4: "+regexBU(src, pat));
}
}
// Memoization vs Tabulation : https://www.geeksforgeeks.org/tabulation-vs-memoization/
// Question Link : https://practice.geeksforgeeks.org/problems/wildcard-pattern-matching/1
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