Today I have done leetcode's August LeetCoding Challenge with cpp.

August LeetCoding Challenge 7

Description

Search a 2D Matrix

You are given an m x n integer matrix matrix with the following two properties:

• Each row is sorted in non-decreasing order.
• The first integer of each row is greater than the last integer of the previous row.

Given an integer target, return true if target is in matrix or false otherwise.

You must write a solution in O(log(m * n)) time complexity.

Example 1:

Input: matrix = [[1,3,5,7],[10,11,16,20],[23,30,34,60]], target = 3
Output: true

Example 2:

Input: matrix = [[1,3,5,7],[10,11,16,20],[23,30,34,60]], target = 13
Output: false

Constraints:

• m == matrix.length
• n == matrix[i].length
• 1 <= m, n <= 100
• -104 <= matrix[i][j], target <= 104

Solution

class Solution {
public:
  bool searchMatrix(vector<vector<int>>& matrix, int target) {
    if(!matrix.size() || !matrix[0].size()) return false;
    int begin = 0, end = matrix.size()-1;
    vector<int> &a = matrix[0];
    while(begin < end) {
      int mid = (begin + end) / 2;
      if(matrix[mid].front() > target) {
        end = mid - 1;
      } else if (matrix[mid].back() < target) {
        begin = mid + 1;
      } else {
        break;
      }
    }
    a = matrix[(begin+end)/2];
    return binary_search(a.begin(), a.end(), target);
  }
};

// Accepted
// 133/133 cases passed ( ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 19.85 % of cpp submissions (9.6 MB)