O(m+n) // from top right;
二分法可以从左下开始 --》 右上
public boolean searchMatrix(int[][] matrix, int target) {
        if(matrix == null || matrix.length < 1 || matrix[0].length <1) {
            return false;
        }
        int col = matrix[0].length-1;
        int row = 0;
        while(col >= 0 && row <= matrix.length-1) {
            if(target == matrix[row][col]) {
                return true;
            } else if(target < matrix[row][col]) {
                col--;
            } else if(target > matrix[row][col]) {
                row++;
            }
        }
        return false;
    }



//Binary Search
public int searchMatrix(int[][] matrix, int target) {
       if(matrix == null || matrix.length == 0 || matrix[0].length == 0) 
       return 0;

       int col = 0;
       int row = matrix[0].length - 1;
       int count = 0;
       while (col < matrix.length && row >=0) {
           if (matrix[col][row] < target) {
               col++;
           }
           else if (matrix[col][row] > target) {
               row--;
           }
           else {
               count++;
               row--;
               col++;
           }
       }
       return count;
    }