【LeetCode 74】Search a 2D Matrix

题目描述

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

思路

从左下角开始搜索，每次可以分到小于的范围或者大于的范围。

代码

class Solution {
public:
    bool searchMatrix(vector<vector<int>>& matrix, int target) {
        if (matrix.empty()) return false;
        int n = matrix.size();
        int m = matrix[0].size();
        int row = n-1;
        int col = 0;
        
        while(row >= 0 && col <= m-1) {
            if (matrix[row][col] == target) return true;
            else if (matrix[row][col] < target) col++;
            else if (matrix[row][col] > target) row--;
        }
        
        return false;
    }
};

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