74. Search a 2D Matrix

O(log(mn)) time O(1) space

class Solution {
public:
    bool searchMatrix(vector<vector<int>>& matrix, int target) {
        if (matrix.empty() || matrix[0].empty())
            return false;
        int m = matrix.size(), n = matrix[0].size(), l = 0, r = m * n - 1;
        while (l <= r) {
            int m = l + (r - l) / 2;
            int x = matrix[m / n][m % n];
            if (x == target) return true;
            if (x < target) {
                l = m + 1;
            } else {
                r = m - 1;
            }
        }
        return false;
    }
};