双指针 ,分区

/**
 *
 * @param A int整型一维数组
 * @param B int整型一维数组
 * @return void
 */
function merge(A, m, B, n) {
  // write code here
  let pn = n - 1,
    pm = m - 1,
    pmn = m + n - 1;
  while (pmn >= 0) {
    if (pn < 0 || pm < 0) {
      if (pm < 0) {
        A[pmn] = B[pn];
        pn--;
      } else {
        A[pmn] =  A[pm];
        pm--;
      }
    } else {
      if (A[pm] > B[pn]) {
        A[pmn] = A[pm];
        pm--;
      } else {
        A[pmn] = B[pn];
        pn--;
      }
    }
    pmn--;
  }

  return A;
}
module.exports = {
  merge: merge,
};