1、超时双指针做法

class Solution {
public:
    int trap(vector<int>& height) {
        int thesize=height.size();
        int cnt=0,l=0,r=thesize-1;     
        while(l<r)
        {
            while(l<r&&height[l]==0) ++l;
            while(l<r&&height[r]==0) --r;
            if(l>=r) break;
            for(int j=l;j<=r;++j)
            {
                if(height[j]==0) ++cnt;
                else --height[j];
            }
        }
        return cnt;
    }
};

 2、空间换时间，哈希表+双指针做法

class Solution {
public:
    int trap(vector<int>& height) {
        int thesize=height.size();
        int cnt=0,l=0,r=thesize-1,t=0;
        int hash[100001]={0};
        for(int i=0;i<thesize;++i) ++hash[height[i]];
        while(l<r)
        {
            while(l<r&&height[l]<=t) 
            {
                --hash[t];
                ++l;
            } 
            while(l<r&&height[r]<=t) 
            {
                --hash[t];
                --r;
            }
            if(l>=r) break;
            cnt+=hash[t];
            ++t;
            hash[t]+=hash[t-1];
        }
        return cnt;
    }
};