leetcode 第74题 Search a 2D Matrix

最新推荐文章于 2022-02-05 09:37:47 发布

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本文介绍了一种在已排序的二维矩阵中高效查找目标值的算法。通过从右上角开始搜索，根据目标值与当前元素的关系进行方向调整，最终判断目标值是否存在。

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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.

思路：我们设从二维矩阵右上角那个元素temp = matrix[0][n-1]开始搜索.然后将target与其比较，若和target相等，则返回true;若比target大，则向下搜索;若比target小，则想左搜索。

java代码实现：

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        int row = matrix.length;
        int col = matrix[0].length;
        int i = 0;
        int j = col -1;
        int temp = matrix[i][j];
        while(true){
            if(temp == target)
                return true;
            else if(temp < target && i < row - 1){
                temp = matrix[++i][col-1];
            }
            else if(temp > target && j > 0){
                temp = matrix[i][--j];
            }
            else
                return false;
        }
    }
}