汉诺塔变种（递归）
每次只允许将圆盘移到中间杆上或从中间杆上移出，不允许直接将圆盘从第一根杆上移到第二根杆上，或直接将圆盘从第三根杆上移到第一根杆上。
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| long long solve(int n)
if (n == 1)
return 2;
else
return 3 * solve(n - 1) + 2;
}
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杨辉三角（递归）
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| int solve(int r, int c)
{
if (r == 1 || c == 1 || r == c)
return 1;
return solve(r - 1, c - 1) + solve(r - 1, c);
}
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全排列
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| const int MAXN = 10;
char s[MAXN];
int vis[MAXN];
char res[MAXN];
void solve(char *s, int cnt)
{
if (cnt == strlen(s))
{
for (int i = 0; i < strlen(res); ++i)
cout << res[i] << ' ';
cout << "\n";
}
for (int i = 0; i < strlen(s); ++i)
{
if (!vis[i])
{
vis[i] = 1;
res[cnt] = s[i];
solve(s, cnt + 1);
vis[i] = 0;
}
}
}
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计算二叉树子树节点个数
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| int solve(int n, int m)
{
if (m > n)
return 0;
int res = 1;
res += solve(n, 2 * m);
res += solve(n, 2 * m + 1);
return res;
}
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分解2的幂次方
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| string solve(int n)
{
stack<int> p;
int exp = 0;
while (n)
{
if (n % 2)
p.push(exp);
exp++;
n /= 2;
}
string res = "";
while (!p.empty())
{
if (p.top() == 0)
res += "2(0)";
else if (p.top() == 1)
res += "2";
else
res += "2(" + solve(p.top()) + ")";
p.pop();
if (!p.empty())
res += "+";
}
return res;
}
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