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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