Find an early martial arts novel whose title I can't remember

The plot was about an old man and his granddaughter living on the top of a dangerous mountain. The granddaughter seemed to have gone down the mountain to collect things. When she came back, her grandfather had already been killed. Her grandfather asked her to push a huge rock on the mountain every day. Under the huge rock, there was something that the martial arts world dreamed of. It seemed to be called the Yin Flag. One day, when she was practicing, she heard someone shouting for help and found a teenager falling on the vine on the cliff. The teenager had a blood feud and wanted to go deep into the mountains and forests to find artists to learn skills and take revenge. After she saved the boy, she taught him martial arts. Because the boy was too old, he learned slowly. The girl scolded him. The boy ran away in a huff and ran into the mountains. He met a peerless master. The former leader of the martial arts world lived in seclusion. After the boy learned martial arts, he went to find the woman. She was no longer there. The special skill that the boy learned was called Flying Feather Sixteen Flips. In the story, there should be a Yin and Yang flag. It was not easy to remember so much.