One hundred people wear a hat. This hat is black and white. Everyone can see the color of the hat in front of everyone, but they can't see themselves and the back.

99 people will survive! ! ! The possibility of survival is 1/2.

The hundredth person counts whether the first ninety-nine people wear odd or even black hats, with odd numbers called "black" and even numbers called "white". Then whether the black hat worn by the person in front of the 99th person is odd or even. If the answer is the same as that taken by the hundredth person in the back, it means that he is wearing a white hat (otherwise the odd number of black hats will change). He shouts "white" and tells the person in front that the black hat is even. Instead, he shouted "black" and told the people in front that the black hat was strange. Everyone in front uses this method to judge the color of their hats and convey the parity of their hats, so that the first 99 people can survive.