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nikitakapoor1919nikitakapoor1919
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Add wildcard pattern matching (TheAlgorithms#2441)
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‎DynamicProgramming/RegexMatching.java‎

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

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