add first ture in js

Author: akgmage

Binary Search/first_true.js

@@ -0,0 +1,38 @@
+/*
+    An array of boolean values is divided into two sections; the left section consists of all false and the 
+    right section consists of all true. Find the First True in a Sorted Boolean Array of the 
+    right section, i.e. the index of the first true element. If there is no true element, return -1.
+    
+    Input: arr = [false, false, true, true, true]
+    Output: 2
+
+    Explanation: first true's index is 2.
+*/
+function findBoundary(arr) {
+  let low = 0; // Initialize the low pointer to the beginning of the array.
+  let high = arr.length - 1; // Initialize the high pointer to the end of the array.
+  let bv = -1; // Initialize bv (boundary value) to -1.
+
+  while (low <= high) {
+    let mid = low + Math.floor((high - low) / 2); // Calculate the middle index.
+
+    if (!arr[mid]) {
+      // If the element at the middle index is 'false',
+      // it means that the last 'true' value should be on the right side.
+      low = mid + 1; // Move the low pointer to the right of mid.
+    } else {
+      // If the element at the middle index is 'true',
+      // update bv to the current middle index and continue searching on the left side.
+      bv = mid; // Update bv to the current middle index.
+      high = mid - 1; // Move the high pointer to the left of mid.
+    }
+  }
+
+  // The loop ends when low > high, indicating that the search is complete.
+  // bv contains the index of the last 'true' value encountered.
+  return bv;
+}
+
+const arr = [false, false, false, true, true, true, true];
+const boundary = findBoundary(arr);
+console.log("Boundary Index:", boundary);