The problem of finding three color flags in C language test 165

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1、 subject

subject ： There's a rope , There's red on it 、 white 、 Flags in three colors of blue . The colors of the flags on the rope are out of order , Now we have to classify the flags , According to blue 、 white 、 In red order . You can only move on the rope , And only two flags can be exchanged at a time , How to move the flag so that it can be moved at least ？：

analysis ：
The flag moves on the rope , And only two flags can be exchanged at a time , So just make sure that when you move the flag , Start at the beginning of the rope , The blue flag moves forward , The white flag is left in the middle , The red flag moves backwards . To minimize the number of moves , You can use three pointers b、w、r As blue flag 、 White and red flags .

if w The current flag pointed by the pointer is white , be w The pointer increases 1, It means adding one side to the white flag . if w The current flag pointed by the pointer is blue , Will b The pointer and w The flags pointed to by the pointer are exchanged , meanwhile b The pointer and w The pointer increases 1, It means that both the blue flag and the white flag have an element . if w The pointer points to