Here is the thought flow: we are trying 'find' the boundary - it is a search, so binary search.

class Solution {  bool isRowHit(vector
      
       
        >& image, int r)  {    int w = image[0].size();    for(int i = 0; i < w; i ++)      if (image[r][i] == '1')    return true;    return false;  }  bool isColHit(vector
        
         
          >& image, int c)  {    int h = image.size();    for(int i = 0; i < h; i ++)      if (image[i][c] == '1')    return true;    return false;  }    int bSearchL2H(function
          
            f, int a, int b)  {    int r = a;    while(a<=b)    {      int mid = (a + b) / 2;      if(f(mid))      {    r = mid;    a = mid + 1;      }      else      {    b = mid - 1;      }    }    return r;      }    int bSearchH2L(function
           
             f, int a, int b) { int r = a; while(a<=b) { int mid = (a + b) / 2; if(f(mid)) { r = mid; b = mid - 1; } else { a = mid + 1; } } return r; }public: int minArea(vector
            
             
              >& image, int x, int y) { int h = image.size(); int w = image[0].size(); auto fr = std::bind(&Solution::isRowHit, this, image, std::placeholders::_1); auto fc = std::bind(&Solution::isColHit, this, image, std::placeholders::_1); int r1 = bSearchL2H(fr, x, h - 1); int r0 = bSearchH2L(fr, 0, x); int h1 = bSearchL2H(fc, y, w - 1); int h0 = bSearchH2L(fc, 0, y); return (h1 - h0 + 1) * (r1 - r0 + 1); }};