225. 用佇列實現棧

class MyStack {
public:
    /** Initialize your data structure here. */
    queue<int> a;
    int k=0;
    
    MyStack() {
        
    }
    
    /** Push element x onto stack. */
    void push(int x) {
        a.push(x);
        k++;
    }

    /** Removes the element on top of the stack and returns that element. */
    int pop() {
        int p=--k;
        while(p--)
        {
            int q=a.front();  
            a.pop();
            a.push(q);
        }
        int q=a.front(); 
        a.pop();
        return q;
    }
    
    /** Get the top element. */
    int top() {
        int p=k;
        int q;
        while(p--)
        {
            q=a.front();  
            a.pop();
            a.push(q);
        }
        return q;        
    }
    
    /** Returns whether the stack is empty. */
    bool empty() {
        return a.empty();   
    }
};

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack obj = new MyStack();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.top();
 * bool param_4 = obj.empty();
 */
 

315. 計算右側小於當前元素的個數

class Solution {
public:     
    vector<int> countSmaller(vector<int>& nums) {
        vector<int> counts(nums.size());
        vector<int> trans;
        if (nums.size() == 0)
            return counts;
        trans.push_back(nums[nums.size() - 1]);
        for (int i = nums.size() - 2; i >= 0; i--) {
            // 這裡二分我們用STL裡的就好了
            auto it = lower_bound(trans.begin(), trans.end(), nums[i]);
            counts[i] = it - trans.begin();
            trans.insert(it, nums[i]);
        }
        return counts;
    }
};