Leetcode-Search a 2D Matrix

Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:

 

• Integers in each row are sorted from left to right.
• The first integer of each row is greater than the last integer of the previous row.

 

For example,

Consider the following matrix:

[
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]

Given target = 3, return true.

写得蛮啰嗦，简而言之就是先搜索列号，再在搜索到的列里面去搜索该元素，全部用的二分查找（反正它已经排序了）

        public boolean searchMatrix(int[][] matrix, int target) {
            if(matrix==null||matrix.length <=0){
                return false;
            }
            int targetRow =0;
            int m = matrix.length;
            int n = matrix[0].length;
            
            //make sure target is in the range
            if(target < matrix[0][0] || target > matrix[m-1][n-1]){
                return false;
            }else{
                targetRow = searchRow(matrix,target,0,m-1);
                if(targetRow == -1){
                    return false;
                }
                return searchElement(matrix,target,targetRow,0,n-1);
            }
            
        }
        public int searchRow(int[][] matrix,int target,int start,int end){
            while(start <= end){
                int mid = (end-start)/2 +start;
                if(matrix[mid][0] == target){
                    return mid;
                }
                if(matrix[mid][0] < target){
                    if(matrix[mid][matrix[0].length -1] >= target){
                        return mid;
                    }else{
                        start  = mid +1;
                        continue;
                    }
                }
                if(matrix[mid][0] > target){
                    end = mid-1;
                    continue;
                }
                
            }
            return -1;
        }
        
        public boolean searchElement(int [][] matrix,int target,int row,int start,int end){
            while(start <= end){
              int mid = (end-start)/2 + start;  
              if( matrix[row][mid] == target){
                 return true;
              }
              if(matrix[row][mid] < target){
                  start = mid+1;
                  continue;
              }
              if(matrix[row][mid] > target){
                  end  = mid - 1;
                  continue;
              }
            }
            return false;
        }