Add borrowing checkbox for subtraction problems

src/index.html

@@ -214,6 +214,14 @@ <h3>How many worksheets?</h3>
         </tr></tbody></table>
         </label>
       </div>
+      <div class="col-md-6 pt-3">
+        <label>
+        <table><tbody><tr>
+          <td><div class="p-3"><input id="borrowingChkbx" class="form-control" type="checkbox"/></div></td>
+          <td><h3 title="Only for subtraction problems. When checked, only generates problems that require borrowing.">Only problems that require borrowing?</h3></td>
+        </tr></tbody></table>
+        </label>
+      </div>
       <div class="col-md-12 pt-3">
         <div class="w-50 ml-auto mr-auto">
           <button class="btn btn-lg btn-primary btn-block p-3" onclick="HwGen.preview()">

src/js/hw-gen.js

@@ -12,6 +12,7 @@ const HwGen = (() => {
   const worksheetSelectView = document.getElementById("worksheetSelectView");
   const worksheetCountSelect = document.getElementById("worksheetCount");
   const answerKeyChkbx = document.getElementById("answerKeyChkbx");
+  const borrowingChkbx = document.getElementById("borrowingChkbx");
   const printConfigView = document.getElementById("printConfigView");
   const worksheetView = document.getElementById("worksheetView");
   const categorySelectView = document.getElementById("categorySelectView");
@@ -23,28 +24,54 @@ const HwGen = (() => {
     "selectedSet": "",
     "selectedCount": 6,
     "showAnswerKey": true,
+    "onlyBorrowing": false,
   };
   let screenshotInterval = null;
   let screenshotNum = 2;
   let tipScrollInterval = null;
   let tipNum = 0;
-  const genEquation = (xSize, ySize, mathSymbol) => {
-    const x = randRangeByDigits(xSize);
-    const y = randRangeByDigits(ySize);
-    const z = solution(x, y, mathSymbol);
+  const genEquation = (xSize, ySize, mathSymbol, onlyBorrowing) => {
+    let x, y, z;
+    let attempts = 0;
+    const maxAttempts = 1000;
+
+    do {
+      x = randRangeByDigits(xSize);
+      y = randRangeByDigits(ySize);
+      z = solution(x, y, mathSymbol);
+      attempts++;
+
+      // For subtraction with borrowing constraint
+      if (mathSymbol === "+" && onlyBorrowing) {
+        // For subtraction problems, we use mathSymbol "+" but solve for y where z - x = y
+        // Check if z - x requires borrowing
+        if (requiresBorrowing(z, x)) {
+          break;
+        }
+      } else {
+        break;
+      }
+    } while (attempts < maxAttempts);
+
     return { x, y, z };
   };
-  const generate = (xSize, ySize, mathSymbol, count, useAllPossible1Digit, myGenEq) => {
+  const generate = (xSize, ySize, mathSymbol, count, useAllPossible1Digit, myGenEq, onlyBorrowing) => {
     let arr = [];
     if (useAllPossible1Digit) {
       SINGLE_DIGITS.map(x => SINGLE_DIGITS.map(y => arr.push({ x, y, z: solution(x, y, mathSymbol) })));
+
+      // Filter for borrowing if needed
+      if (onlyBorrowing && mathSymbol === "+") {
+        arr = arr.filter(eq => requiresBorrowing(eq.z, eq.x));
+      }
+
       arr.sort(() => Math.random() - 0.5); //shuffle
       arr.sort(() => Math.random() - 0.5); //shuffle
       if (count < arr.length) arr = arr.slice(0, count);
     }
     else {
       for (let i = 0; i < count; i++) {
-        arr.push(myGenEq ? myGenEq() : genEquation(xSize, ySize, mathSymbol));
+        arr.push(myGenEq ? myGenEq() : genEquation(xSize, ySize, mathSymbol, onlyBorrowing));
       }
     }
     return arr;
@@ -119,7 +146,7 @@ const HwGen = (() => {
     worksheetList.innerHTML = `<h3>Select ${data["selectedCat"]} Worksheet</h3>` +
       hwMap[data["selectedCat"]].map((hwSet, i) => {
         const {title, xSize, ySize, mathSymbol, outputFunc, count, name, long, useAllPossible1Digit, myGenEq, myGenEqList} = hwSet;
-        const eq = myGenEq ? myGenEq() : myGenEqList ? myGenEqList()[0] : genEquation(xSize, ySize, mathSymbol);
+        const eq = myGenEq ? myGenEq() : myGenEqList ? myGenEqList()[0] : genEquation(xSize, ySize, mathSymbol, false);
         const eqStr = outputFunc(eq, -1, 0, long);
         return `${i === 0 ? '' : '<hr/>'}<div class="row">
         <div class="col-1 text-right pr-0 text-sm">
@@ -152,10 +179,12 @@ const HwGen = (() => {
     }
     const { title, count, columns, xSize, ySize, mathSymbol, myGenEqList, outputFunc, answerKey, long, answerSpace, useAllPossible1Digit, myGenEq } = hwSet;
     worksheetsDiv.innerHTML = "";
+    // Only apply borrowing filter for subtraction problems
+    const onlyBorrowing = data['onlyBorrowing'] && data['selectedCat'] === 'Subtraction';
     for (let i = 0; i < data['selectedCount']; i++) {
       const worksheet = worksheetOrig.cloneNode(true)
         , output = worksheet.querySelector(".output")
-        , eqList = myGenEqList ? myGenEqList() : generate(xSize, ySize, mathSymbol, count, useAllPossible1Digit, myGenEq)
+        , eqList = myGenEqList ? myGenEqList() : generate(xSize, ySize, mathSymbol, count, useAllPossible1Digit, myGenEq, onlyBorrowing)
         , titleDiv = worksheet.querySelector(".title")
         , outputStr = eqList.map((eq, i) => outputFunc(eq, i, columns, long, answerSpace)).join("")
         , emoji = randArr(emojis)
@@ -206,6 +235,7 @@ const HwGen = (() => {
     }
     data['selectedCount'] = worksheetCountSelect ? parseInt(worksheetCountSelect.value) : 1;
     data['showAnswerKey'] = answerKeyChkbx.checked ? true : false;
+    data['onlyBorrowing'] = borrowingChkbx && borrowingChkbx.checked ? true : false;
   };
   const init = () => {
     const hwSetName = getUrlParam("set");

src/js/util.js

@@ -24,6 +24,20 @@ const solution = (x, y, mathSymbol) => {
     default: return x + y;
   }
 };
+const requiresBorrowing = (minuend, subtrahend) => {
+  const minuendStr = String(minuend);
+  const subtrahendStr = String(subtrahend);
+  const maxLen = Math.max(minuendStr.length, subtrahendStr.length);
+
+  for (let i = 0; i < maxLen; i++) {
+    const minuendDigit = parseInt(minuendStr[minuendStr.length - 1 - i] || 0);
+    const subtrahendDigit = parseInt(subtrahendStr[subtrahendStr.length - 1 - i] || 0);
+    if (minuendDigit < subtrahendDigit) {
+      return true;
+    }
+  }
+  return false;
+};
 const getUrlParam = param => {
   const paramMap = {};
   const urlArr = document.location.href.split("?");