Merge pull request #104 from PresenceOP-Coder/rabinkarp

feat: implemented rabin karp

Author: adityacosmos24

src/algorithms/searching/RabinKarp.js

@@ -0,0 +1,147 @@
+export function getRabinKarpSteps(text, pattern) {
+    const steps = [];
+    const n = text.length;
+    const m = pattern.length;
+
+    if (m === 0 || n < m) {
+        return { steps, found: false };
+    }
+
+    const d = 256; 
+    const q = 101; 
+    let h = 1; 
+    let pHash = 0;
+    let tHash = 0; 
+    let found = false;
+
+    for (let i = 0; i < m - 1; i++) {
+        h = (h * d) % q;
+    }
+
+    steps.push({
+        windowStart: 0,
+        compareIndex: -1,
+        status: 'calculating',
+        pHash: 0,
+        tHash: 0,
+        message: `Starting. Pattern length=${m}, Text length=${n}. Prime q=${q}. Multiplier h=${h}.`
+    });
+
+    for (let i = 0; i < m; i++) {
+        pHash = (d * pHash + pattern.charCodeAt(i)) % q;
+        tHash = (d * tHash + text.charCodeAt(i)) % q;
+        
+        steps.push({
+            windowStart: 0,
+            compareIndex: i,
+            status: 'calculating',
+            pHash,
+            tHash,
+            message: `Calculating initial hashes. Index ${i}. Pattern Hash = ${pHash}, Window Hash = ${tHash}.`
+        });
+    }
+
+    for (let i = 0; i <= n - m; i++) {
+        steps.push({
+            windowStart: i,
+            compareIndex: -1,
+            status: 'sliding',
+            pHash,
+            tHash,
+            message: `Sliding window to index ${i}. Pattern Hash = ${pHash}, Window Hash = ${tHash}.`
+        });
+
+        if (pHash === tHash) {
+            steps.push({
+                windowStart: i,
+                compareIndex: 0,
+                status: 'hash_match',
+                pHash,
+                tHash,
+                message: `Hash Match Found! Verifying character by character...`
+            });
+
+            let j = 0;
+            for (j = 0; j < m; j++) {
+                steps.push({
+                    windowStart: i,
+                    compareIndex: i + j,
+                    patternCompareIndex: j,
+                    status: 'verifying',
+                    pHash,
+                    tHash,
+                    message: `Verifying: text[${i + j}] ('${text[i + j]}') === pattern[${j}] ('${pattern[j]}')?`
+                });
+
+                if (text[i + j] !== pattern[j]) {
+                    steps.push({
+                        windowStart: i,
+                        compareIndex: i + j,
+                        patternCompareIndex: j,
+                        status: 'spurious_hit',
+                        pHash,
+                        tHash,
+                        message: `Spurious Hit! Mismatch found. Resuming search.`
+                    });
+                    break;
+                }
+            }
+
+            if (j === m) {
+                found = true;
+                steps.push({
+                    windowStart: i,
+                    compareIndex: -1,
+                    status: 'found',
+                    pHash,
+                    tHash,
+                    message: `Pattern Found at index ${i}!`
+                });
+            }
+        }
+
+        if (i < n - m) {
+            const oldHash = tHash;
+            const charToRemove = text.charCodeAt(i);
+            const charToAdd = text.charCodeAt(i + m);
+            
+            tHash = (d * (tHash - charToRemove * h) + charToAdd) % q;
+            if (tHash < 0) {
+                tHash += q;
+            }
+
+            steps.push({
+                windowStart: i,
+                compareIndex: -1,
+                status: 'rolling',
+                removeIndex: i,
+                addIndex: i + m,
+                pHash,
+                tHash: oldHash,
+                message: `Rolling hash... Removing '${text[i]}' (val ${charToRemove}).`
+            });
+            
+            steps.push({
+                windowStart: i + 1,
+                compareIndex: -1,
+                status: 'rolling',
+                removeIndex: i,
+                addIndex: i + m,
+                pHash,
+                tHash,
+                message: `Rolling hash... Adding '${text[i + m]}' (val ${charToAdd}). New Window Hash = ${tHash}.`
+            });
+        }
+    }
+
+    steps.push({
+        windowStart: -1,
+        compareIndex: -1,
+        status: found ? 'finished_found' : 'finished_not_found',
+        pHash,
+        tHash,
+        message: found ? "Search complete. Pattern was found." : "Search complete. Pattern was not found."
+    });
+
+    return { steps, found };
+}