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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.
分析：将二维数组看为一个一维sorted数组，然后用bianry search。时间复杂度为O(log(m*n)),代码如下：
1 class Solution { 2 public: 3 bool searchMatrix(vector<vector<int> > &matrix, int target) { 4 int m = matrix.size(); 5 if(m == 0) return false; 6 int n = matrix[0].size(); 7 if(n == 0) return false; 8 9 int l = 0, r = m * n - 1;10 while(l <= r){11 int mid = (l + r)/2;12 int row = mid/n, col = mid%n;13 if(matrix[row][col] == target) return true;14 if(matrix[row][col] < target) l = mid + 1;15 else r = mid - 1;16 }17 18 return false;19 }20 };
Leetcode:Search a 2D Matrix
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