19.2.13 [LeetCode 74] 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.

Example 1:

Input:
matrix = [
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]
target = 3
Output: true

Example 2:

Input:
matrix = [
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]
target = 13
Output: false

题意

用矩阵来存储有序序列，高效查找某值

题解

class Solution {
public:
    bool searchMatrix(vector<vector<int>>& matrix, int target) {
        if (matrix.empty()||matrix[0].empty())return false;
        int m = matrix.size(), n = matrix[0].size();
        for (int i = 0; i < m; i++) {
            if (matrix[i][n - 1] < target)continue;
            int s = 0, e = n - 1;
            while (s <= e) {
                int mid = (s + e) / 2;
                if (matrix[i][mid] < target)
                    s = mid + 1;
                else
                    e = mid - 1;
            }
            if (matrix[i][s] == target)
                return true;
            else return false;
        }
        return false;
    }
};