Create array-equal-split-index.js

array-equal-split-index.js

@@ -0,0 +1,41 @@
+
+const findIndex = (arr) => {
+  if (arr.length === 1 || arr.length === 2) {
+    console.log(`no index for arr with length ${arr.length}`);
+    return;
+  }
+
+  const sum = arr.reduce((acc, val) => acc + val, 0);
+
+  let leftSum = 0,
+    rightSum = sum - arr[0],
+    index = 1,
+    missingIndex = 0;
+
+  while (index < arr.length) {
+
+    // console.log(`${index} => ${leftSum}, ${rightSum}`);
+    if (leftSum === rightSum) {
+      // console.log('found index');
+      missingIndex = index - 1;
+      break;
+    }
+    rightSum = rightSum - arr[index];
+    leftSum = leftSum + arr[index - 1];
+    index = index + 1;
+  }
+
+
+  if (missingIndex === 0) {
+    console.log('no such index');
+  } else {
+    console.log(missingIndex);
+  }
+};
+
+findIndex([1]);
+findIndex([1, 2]);
+findIndex([1, 2, 3]); // no index
+findIndex([2, 2, 2]); // index at 1
+findIndex([1, 2, 3, 4, 10, 9, 5, 5, 4, 6]); // index at 5
+