[LeetCode]Search a 2D Matrix II

题目

Number: 240
Difficulty: Medium
Tags: Divide and Conquer, Binary Search

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 in ascending from left to right.
Integers in each column are sorted in ascending from top to bottom.

For example,

Consider the following matrix:

[
  [1,   4,  7, 11, 15],
  [2,   5,  8, 12, 19],
  [3,   6,  9, 16, 22],
  [10, 13, 14, 17, 24],
  [18, 21, 23, 26, 30]
]

Given target = 5, return true.

Given target = 20, return false.

题解

在一个每一行是排序，每一列是排序的矩阵中查找数字。

参考《剑指Offer》面试题3.

代码

bool searchMatrix(vector<vector<int>>& matrix, int target) {
    if(matrix.empty())
        return false;
    int r = matrix.size(), c = matrix[0].size();
    int i = 0, j = c - 1;
    while(i < r && j >= 0){
        if(matrix[i][j] == target)
            return true;
        else if(matrix[i][j] > target)
            j--;
        else
            i++;
    }
    return false;
}