【单调栈】lc503. 下一个更大元素 II lc84. 柱状图中最大的矩形 lc85. 最大矩形

.

• ​​[503. 下一个更大元素 II](https://leetcode-cn.com/problems/next-greater-element-ii/)​​
• ​​[84. 柱状图中最大的矩形](https://leetcode-cn.com/problems/largest-rectangle-in-histogram/submissions/)​​
• ​​[85. 最大矩形](https://leetcode-cn.com/problems/maximal-rectangle/)​​

503. 下一个更大元素 II

#define debug(x) cout<<#x<<": "<<(x)<<endl;

class Solution {
public:
    vector<int> nextGreaterElements(vector<int>& a) {
        stack<int> st;
        int n = a.size();
        vector<int> ret(n,-1);
        deque<int> qu;
        qu.push_back(0);
        for(int i=1;i<n;++i){
            if(a[i] <= a[qu.back()]){
                qu.push_back(i);
            }else{
                while( !qu.empty() && a[i] > a[qu.back()] ){
                    ret[qu.back()] = a[i];
                    qu.pop_back();
                }
                qu.push_back(i);
            }
        }

        for(int i=0;i<n;++i){
            
            if(i==qu.back()){
                break;
            }
            if(a[i] <= a[qu.back()]){
                qu.push_back(i);
            }else{
                while( !qu.empty() && a[i] > a[qu.back()] ){
                    ret[qu.back()] = a[i];
                    qu.pop_back();
                }
            }
        }
        return ret;
    }
};

84. 柱状图中最大的矩形

class Solution {
public:
    int largestRectangleArea(vector<int>& h) {
        stack<int> st;
        int ret = 0;
        int n = h.size();
        for(int i=0;i<n;++i){
            if(st.empty() || h[i] >= h[st.top()]){
                st.push(i);
            }else{
                
                while(!st.empty() && h[i] < h[st.top()] ){
                    int hei = h[st.top()];
                    st.pop();
                    int wid = i;
                    if(!st.empty()){
                        wid = wid - st.top() -1;
                    }
                    ret = max(ret,hei*wid);
                }
                st.push(i);
            }
        }

        while(!st.empty()){
            int hei = h[st.top()];
            st.pop();
            int wid = n;
            if(!st.empty()){
                wid = wid - st.top() -1;
            }
            ret = max(ret,hei*wid);
        }
        return ret;
    }
};

85. 最大矩形

class Solution {
public:
    int maximalRectangle(vector<vector<char>>& a) {
        int n = a.size();
        int m = a[0].size();
        vector<int> h(m,0);
        int ret=0;
        for(int i=0;i<n;++i){
            for(int j=0;j<m;++j){
                if( a[i][j] == '0' ){
                    h[j] = 0;
                }else{
                    h[j] += 1;
                }
            }
            stack<int> st;
            for(int j=0;j<m;++j){
                if(st.empty() || h[j] >= h[st.top()]){
                    st.push(j);
                }else{
                    while( !st.empty() && h[j] < h[st.top()] ){
                        int hei = h[st.top()];
                        st.pop();
                        int wid = j;
                        if(!st.empty()){
                            wid = wid - st.top() - 1;
                        }
                        ret = max(ret,hei*wid);
                    }
                    st.push(j);
                }
            }

            while(!st.empty()){
                int hei = h[st.top()];
                st.pop();
                int wid = m;
                if(!st.empty()){
                    wid = wid - st.top() - 1;
                }
                ret = max(ret,hei*wid);
            }
        }
        
        return ret;
    }
};