Merge pull request #41 from atulya-srivastava/levenshtein-distance-algo

Levenshtein distance algorithm implementation

Author: adityacosmos24

src/App.jsx

@@ -4,6 +4,7 @@ import { BrowserRouter as Router, Routes, Route } from "react-router-dom";
 import SortingPage from "./pages/sorting/SortingPage";
 import GraphPage from "./pages/graph/GraphPage";
 import Homepage from "./pages/Homepage.jsx";
+import DynamicProgrammingPage from "./pages/dynamic-programming/DyanmicProgrammingPage.jsx";
 
 function App() {
   return (
@@ -13,6 +14,7 @@ function App() {
         {/* <Route path="/graph/union-find" element={<UnionFindPage />} /> */}
         <Route path="/sorting" element={<SortingPage />} />
         <Route path="/graph" element={<GraphPage />} />
+        <Route path="/dynamic-programming" element={<DynamicProgrammingPage />} />
       </Routes>
     </Router>
   );

src/algorithms/dynamic-programming/levenshtein.js

@@ -0,0 +1,236 @@
+const calculateLevenshtein = (s1, s2, costs) => {
+  const m = s1.length;
+  const n = s2.length;
+  const dp = Array(m + 1)
+    .fill(null)
+    .map(() => Array(n + 1).fill(null));
+
+  for (let i = 0; i <= m; i++) dp[i][0] = i * costs.delete;
+  for (let j = 0; j <= n; j++) dp[0][j] = j * costs.insert;
+
+  for (let i = 1; i <= m; i++) {
+    for (let j = 1; j <= n; j++) {
+      if (s1[i - 1] === s2[j - 1]) {
+        dp[i][j] = dp[i - 1][j - 1];
+      } else {
+        dp[i][j] = Math.min(
+          dp[i - 1][j] + costs.delete,
+          dp[i][j - 1] + costs.insert,
+          dp[i - 1][j - 1] + costs.replace
+        );
+      }
+    }
+  }
+  return dp;
+};
+
+const getExplanation = (s1, s2, i, j, dp, costs) => {
+  if (i === 0) {
+    return {
+      title: `Base case: Converting empty string to "${s2.substring(0, j)}"`,
+      text: `We need ${j} insertions. Cost = ${j} × ${costs.insert} = ${
+        j * costs.insert
+      }`,
+    };
+  }
+  if (j === 0) {
+    return {
+      title: `Base case: Converting "${s1.substring(0, i)}" to empty string`,
+      text: `We need ${i} deletions. Cost = ${i} × ${costs.delete} = ${
+        i * costs.delete
+      }`,
+    };
+  }
+
+  const char1 = s1[i - 1];
+  const char2 = s2[j - 1];
+  const match = char1 === char2;
+  const deletion = dp[i - 1][j] + costs.delete;
+  const insertion = dp[i][j - 1] + costs.insert;
+  const substitution = dp[i - 1][j - 1] + (match ? 0 : costs.replace);
+
+  let title = `Cell [${i}][${j}]: Comparing '${char1}' with '${char2}'`;
+  let text = "";
+
+  if (match) {
+    text = `Characters match! We can skip (no operation).\n• Skip (diagonal): ${
+      dp[i - 1][j - 1]
+    } + 0 = ${substitution}\n• Delete '${char1}' (down): ${dp[i - 1][j]} + ${
+      costs.delete
+    } = ${deletion}\n• Insert '${char2}' (right): ${dp[i][j - 1]} + ${
+      costs.insert
+    } = ${insertion}\n✓ Best choice: Skip with cost = ${dp[i][j]}`;
+  } else {
+    text = `Characters don't match. We have three options:\n• Replace '${char1}' with '${char2}' (diagonal): ${
+      dp[i - 1][j - 1]
+    } + ${costs.replace} = ${substitution}\n• Delete '${char1}' (down): ${
+      dp[i - 1][j]
+    } + ${costs.delete} = ${deletion}\n• Insert '${char2}' (right): ${
+      dp[i][j - 1]
+    } + ${costs.insert} = ${insertion}\n`;
+    const minCost = dp[i][j];
+    let chosenOp = "";
+    if (
+      substitution === minCost &&
+      substitution <= deletion &&
+      substitution <= insertion
+    ) {
+      chosenOp = "Replace (diagonal)";
+    } else if (insertion === minCost && insertion < deletion) {
+      chosenOp = "Insert (right)";
+    } else if (deletion === minCost) {
+      chosenOp = "Delete (down)";
+    }
+    text += `✓ Best choice: ${chosenOp} with cost = ${minCost}`;
+  }
+  return { title, text };
+};
+
+const backtrackOperations = (s1, s2, dp, costs) => {
+  const operations = [];
+  const pathCells = [];
+  let i = s1.length;
+  let j = s2.length;
+
+  pathCells.push([i, j]);
+
+  while (i > 0 || j > 0) {
+    let op;
+    if (i === 0) {
+      op = {
+        op: "insert",
+        char: s2[j - 1],
+        pos: i,
+        cells: [
+          [i, j],
+          [i, j - 1],
+        ],
+      };
+      operations.unshift(op);
+      j--;
+    } else if (j === 0) {
+      op = {
+        op: "delete",
+        char: s1[i - 1],
+        pos: i,
+        cells: [
+          [i, j],
+          [i - 1, j],
+        ],
+      };
+      operations.unshift(op);
+      i--;
+    } else if (s1[i - 1] === s2[j - 1]) {
+      op = {
+        op: "skip",
+        char: s1[i - 1],
+        pos: i,
+        cells: [
+          [i, j],
+          [i - 1, j - 1],
+        ],
+      };
+      operations.unshift(op);
+      i--;
+      j--;
+    } else {
+      const repCost = dp[i - 1][j - 1] + costs.replace;
+      const insCost = dp[i][j - 1] + costs.insert;
+      const delCost = dp[i - 1][j] + costs.delete;
+
+      if (repCost <= delCost && repCost <= insCost) {
+        op = {
+          op: "replace",
+          from: s1[i - 1],
+          to: s2[j - 1],
+          pos: i,
+          cells: [
+            [i, j],
+            [i - 1, j - 1],
+          ],
+        };
+        operations.unshift(op);
+        i--;
+        j--;
+      } else if (insCost < delCost) {
+        op = {
+          op: "insert",
+          char: s2[j - 1],
+          pos: i,
+          cells: [
+            [i, j],
+            [i, j - 1],
+          ],
+        };
+        operations.unshift(op);
+        j--;
+      } else {
+        op = {
+          op: "delete",
+          char: s1[i - 1],
+          pos: i,
+          cells: [
+            [i, j],
+            [i - 1, j],
+          ],
+        };
+        operations.unshift(op);
+        i--;
+      }
+    }
+    pathCells.push([i, j]);
+  }
+
+  return { operations, path: pathCells };
+};
+
+const processOperations = (ops, s1) => {
+  let currentString = s1;
+  return ops
+    .map((op) => {
+      const displayString = currentString;
+      const actualPos = op.pos - (s1.length - currentString.length);
+
+      let displayText = "";
+      if (op.op === "replace") {
+        displayText = `${displayString}: replace ${
+          currentString[actualPos - 1]
+        } with ${op.to} at position ${actualPos}`;
+        currentString =
+          currentString.substring(0, actualPos - 1) +
+          op.to +
+          currentString.substring(actualPos);
+      } else if (op.op === "delete") {
+        displayText = `${displayString}: delete ${
+          currentString[actualPos - 1]
+        } at position ${actualPos}`;
+        currentString =
+          currentString.substring(0, actualPos - 1) +
+          currentString.substring(actualPos);
+      } else if (op.op === "insert") {
+        displayText = `${displayString}: insert ${op.char} at position ${actualPos}`;
+        currentString =
+          currentString.substring(0, actualPos) +
+          op.char +
+          currentString.substring(actualPos);
+      } else if (op.op === "skip") {
+        displayText = `${displayString}: don't change ${op.char} at position ${actualPos}`;
+      }
+
+      return { ...op, displayText, isSkip: op.op === "skip" };
+    })
+    .concat([
+      {
+        displayText: `${currentString}: (final result)`,
+        isFinal: true,
+        cells: [],
+      },
+    ]);
+};
+
+export {
+  calculateLevenshtein,
+  getExplanation,
+  backtrackOperations,
+  processOperations,
+};