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240. Search a 2D Matrix II

{leetcode}/problems/search-a-2d-matrix-ii/[LeetCode - Search a 2D Matrix II^]

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.

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.

思路分析

不能对真个矩阵进行二分查找！可以对单行做二分查找。

从右上角开始搜索，小则下移，大则左移，这个方案真是精妙！

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一刷
link:{sourcedir}/_0240_SearchA2DMatrixII.java[role=include]
二刷
link:{sourcedir}/_0240_SearchA2DMatrixII_2.java[role=include]