algorithm: move to a dedicated directory

src/algorithm/index.ts

@@ -0,0 +1,51 @@
+/**
+ * Performs a binary search within a specified range.
+ * @param begin The starting index of the search range.
+ * @param end The ending index of the search range.
+ * @param beforeHalf A list of predicates indicating conditions before the midpoint.
+ * @returns A tuple containing the indices representing the binary search state: [begin, half, end].
+ */
+export function binSearch(begin: number, end: number, beforeHalf: boolean[]): [number, number, number] {
+    const gHalf = () => { return Math.floor((end - begin) / 2) + begin; };
+
+    for (const pred of beforeHalf) {
+        const half = gHalf();
+        if (pred) {
+            // Happens before "half"
+            end = half;
+        } else {
+            begin = half;
+        }
+    }
+
+    const half = gHalf();
+    console.log(`Checking range: [${begin}, ${end}), ${end - begin} objects, mid ${half}`);
+
+    return [begin, half, end];
+}
+
+export async function autoBisect(
+    begin: number,
+    end: number,
+    check: (
+        begin: number,
+        end: number,
+        index: number
+    ) => Promise<boolean>) {
+
+    // Try to find the first index where check() predicates to true.
+    // Assume check() is true at first, for range [begin, end)
+    let index = 0;
+    while (end - begin > 1) {
+        const mid = Math.floor((end - begin) / 2) + begin;
+        if (await check(begin, mid, index)) {
+            // Shrink half range.
+            end = mid;
+        } else {
+            begin = mid;
+        }
+        index++;
+    }
+
+    return begin;
+}