[leetcode] Maximal Square_stcol 和 stcolop 、 strowcol-优快云博客

本文链接：https://blog.youkuaiyun.com/lmxmimihuhu/article/details/46368055

本文介绍了一个经典的编程问题——最大正方形问题，即在一个由0和1填充的二维矩阵中找到包含全1的最大正方形，并返回其面积。文章提供了两种解决方案，一种使用Java实现，另一种使用C++实现。

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From ： https://leetcode.com/problems/maximal-square/

Given a 2D binary matrix filled with 0's and 1's, find the largest square containing all 1's and return its area.

For example, given the following matrix:

Return 4.

public class Solution {
    public int maximalSquare(char[][] matrix) {
        if(matrix == null || matrix.length == 0) {
            return 0;
        }
        int max = 0, m = matrix.length, n = matrix[0].length;  
        for(int i=0; i<m && (m-i)*(m-i)>max; ++i) {  
            for(int j=0; j<n && (n-j)*(n-j)>max; j++) {
                if(matrix[i][j] == '1') {
                    int a = area(matrix, i, j, m, n, max);
                    if(a > max) {
                        max = a;
                    }
                }
            }  
        }  
        return max;  
    }  
    
    private int area(char[][] mt, int sti, int stj, int m, int n, int max) {
        int i=sti, a=0;
        int l = n; // minimum length
        while(i < m) {
            // boundry
            int k = i-sti+1;
            
            int j = stj;
            while(j<n && mt[i][j]!='0') {
                ++j;
            }
            if(j-stj < l) {
                l = j-stj;
            }
            
            // area
            int ta = l*l;
            if(k < l) {
                ta = k*k;
            }
            if(ta > a) {
                a = ta;
            }
            // try stop
            if(k >= l || l*l <= max) {
                break;
            }
            ++i;
        }
        return a;
    }
}

class Solution {
public:
	void checkSquare(vector<vector<char>>& matrix, int stRow, int stCol,int rows, int cols, int& max) {
		int j, i=stRow, col = cols;
		while(i < rows) {
			j = stCol;
			while(j<cols && matrix[i][j]!='0') j++;
			if((j-stCol)*(j-stCol) <= max) return;
            if(j-stCol < col) col = j-stCol;
			if(++i-stRow>col) return;
            if((i-stRow)*(i-stRow) > max) max = (i-stRow)*(i-stRow);
        }
	}

	int maximalSquare(vector<vector<char>>& matrix) {
        int max = 0, rows = matrix.size(), cols;
        for(int i=0; i<rows; i++) {
            cols = matrix[i].size();
            if((rows-i)*(rows-i) <= max || cols*cols  <=  max) continue;
            for(int j=0; j<cols; j++) {
                if((rows-i)*(cols-j) <= max) break;
                checkSquare(matrix, i, j, rows, cols, max);
            }
        }
        return max;
    }
};