playwright/packages/playwright-core/src/utils/sequence.ts

/**
 * Copyright (c) Microsoft Corporation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

export function findRepeatedSubsequences(s: string[]): { sequence: string[]; count: number }[] {
  const n = s.length;
  const result = [];
  let i = 0;

  const arraysEqual = (a1: string[], a2: string[]) => {
    if (a1.length !== a2.length) return false;
    for (let j = 0; j < a1.length; j++) {
      if (a1[j] !== a2[j]) return false;
    }
    return true;
  };

  while (i < n) {
    let maxRepeatCount = 1;
    let maxRepeatSubstr = [s[i]]; // Initialize with the element at index i
    let maxRepeatLength = 1;

    // Try substrings of length from 1 to the remaining length of the array
    for (let p = 1; p <= n - i; p++) {
      const substr = s.slice(i, i + p); // Extract substring as array
      let k = 1;

      // Count how many times the substring repeats consecutively
      while (
        i + p * k <= n &&
        arraysEqual(s.slice(i + p * (k - 1), i + p * k), substr)
      ) {
        k += 1;
      }
      k -= 1; // Adjust k since it increments one extra time in the loop

      // Update the maximal repeating substring if necessary
      if (k > 1 && (k * p) > (maxRepeatCount * maxRepeatLength)) {
        maxRepeatCount = k;
        maxRepeatSubstr = substr;
        maxRepeatLength = p;
      }
    }

    // Record the substring and its count
    result.push({ sequence: maxRepeatSubstr, count: maxRepeatCount });
    i += maxRepeatLength * maxRepeatCount; // Move index forward
  }

  return result;
}