leetcode 较难题II

1.solve数独

dfs

class Solution
{
public:
	bool isValid(vector<vector<char> > &board, int x, int y)
	{
		int i, j;
		for (i = 0; i < 9; i++)
			if (i != x && board[i][y] == board[x][y])
				return false;
		for (j = 0; j < 9; j++)
			if (j != y && board[x][j] == board[x][y])
				return false;
		for (i = 3 * (x / 3); i < 3 * (x / 3 + 1); i++)
			for (j = 3 * (y / 3); j < 3 * (y / 3 + 1); j++)
				if (i != x && j != y && board[i][j] == board[x][y])
					return false;
		return true;
	}
	bool solveSudoku(vector<vector<char> > &board)
	{
		for (int i = 0; i < 9; ++i)
			for (int j = 0; j < 9; ++j)
			{
				if ('.' == board[i][j])
				{
					for (int k = 1; k <= 9; ++k)
					{
						board[i][j] = '0' + k;
						if (isValid(board, i, j) && solveSudoku(board))
							return true;
						board[i][j] = '.';
					}
					return false;
				}
			}
		return true;
	}
};

 2.Longest Valid Parentheses

class Solution {
public:
    int longestValidParentheses(string s) 
    { 
        stack<int> left;//position of '(' 
        for(int ii = 0; ii < s.size(); ++ii){ 
            if (s[ii] == '(') left.push(ii); 
            else if (!left.empty()){//')' 
                s[ii] = 'k'; 
                s[left.top()] = 'k'; 
                left.pop(); 
            } 
        } 
        int maxLength = 0; 
        int length = 0; 
        for(int ii = 0; ii < s.size(); ++ii){ 
            if (s[ii]=='k'){ 
                ++length;                 
                if (maxLength < length) maxLength = length; 
            } 
            else length = 0; 
        } 
        return maxLength; 
    }
};