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]
]

思想：两次二分查找

1. bool searchMatrix(vector<vector<int> > &matrix, int target) {
3. int row=matrix.size();
4. if(row==0) return false;
5. int col=matrix[0].size();
6. if(col==0) return false;
7. int low=0;
8. int end=row-1;
9. int line=-1;
10. bool flag=false;
11. int mid=0;
12. while(low<=end) {
13. mid=low+(end-low)/2;
14. if(target==matrix[mid][0]) {
15. line=mid;
16. flag=true;
17. break;
18. }
19. if(target<matrix[mid][0]) {
20. end=mid-1;
21. } else {
22. low=mid+1;
23. }
24. }
25. if(flag) {
26. return true;
27. } else {
28. line=end;
29. }
30. if(line<0) return false;
31. //if(line==row) line=row-1;
32. low=0;
33. end=col-1;
34. while(low<=end) {
35. mid=low+(end-low)/2;
36. if(target==matrix[line][mid]) {
37. //line=mid;
38. return true;
39. }
40. if(target<matrix[line][mid]) {
41. end=mid-1;
42. } else {
43. low=mid+1;
44. }
45. }
46. return false;
47. }