littledian · November 14, 2018 11:53 · Nov 14, 2018
diff --git a/calculate24.js b/calculate24.js
@@ -0,0 +1,51 @@
+function canCalculate24 (...args) {
+  const length = args.length
+  if (length === 2) {
+    const [ a, b ] = args
+    let result = (a + b === 24) || (a * b === 24) || (Math.abs(a - b) === 24) || (a > b ? a / b === 24 : b / a === 24)
+    return result
+  } else {
+    for (let i = 0; i < length; i++) {
+      for (let j = i + 1; j < length; j++) {
+        const sub = []
+        for (let p = 0; p < i; p++) {
+          sub.push(args[p])
+        }
+        for (let p = i + 1; p < j; p++) {
+          sub.push(args[p])
+        }
+        for (let p = j + 1; p < length; p++) {
+          sub.push(args[p])
+        }
+        const a = args[i]
+        const b = args[j]
+        let temp = a + b
+        if (canCalculate24(temp, ...sub)) return true
+        temp = Math.abs(a - b)
+        if (canCalculate24(temp, ...sub)) return true
+        temp = a * b
+        if (canCalculate24(temp, ...sub)) return true
+        temp = a / b
+        if (canCalculate24(temp, ...sub)) return true
+        temp = b / a
+        if (canCalculate24(temp, ...sub)) return true
+      }
+    }
+    return false
+  }
+}
+
+const result = []
+for (let i = 1; i < 14; i++) {
+  for (let j = i; j < 14; j++) {
+    for (let p = j; p < 14; p++) {
+      for (let q = p; q < 14; q++) {
+        if (!canCalculate24(i, j, p, q)) {
+          result.push([i, j, p, q])
+        }
+      }
+    }
+  }
+}
+
+console.log(result.length)