题解 | #小乐乐走台阶#

#include <stdio.h>

int main() {
    /*
    x * 1   y * 2
    1       ->1

    1 1     ->2

    1 1 1   ->3
    1 2
    2 1

    1 1 1 1 ->5
    2 1 1
    1 2 1
    1 1 2
    2 2               

    1 1 1 1 1   ->8
    2 1 1 1
    1 2 1 1
    1 1 2 1
    1 1 1 2
    2 2 1
    1 2 2
    2 1 2

    1 2 3 5 8 13 21 34 55 89 
    */
    int step;
    scanf("%d", &step);
    int a = 0, b = 1, c = 0;    // 过去2，现在，过去1;
    /*
    step = 1 b = 1,
    step = 2 b = 1, -> a = 2, b = 2, ->
    */
    while (step) {
        c = a;
        a = b;
        b = a + c;
        
        step--;
    }

    printf("%d", b);

    return 0;
}