将n视为根 ，然后深搜算法，在每次递归时候进行检测是否超过了m；未超过则cnt+1；超过则返回；最后cnt即为结果

#include <iostream> 

using namespace std;
int n, m, cnt = 0;

typedef struct Mtree {
    int val;
    struct Mtree* ltree, * rtree;

} mtree;
mtree root1;
void dfs(mtree* rt, int val) {
    rt->val = val;
    if (val <= m) {
        cnt += 1;
        rt->ltree = new mtree;
        rt->rtree = new mtree;
    }
    else return;

    dfs(rt->ltree, val * 2);
    dfs(rt->rtree, val * 2 + 1);
}

int main() {
    while (scanf("%d%d", &n, &m) != EOF)
    {
        cnt = 0;
        mtree t1;
        dfs(&t1, n);
        printf("%d\n", cnt);
    }
}