Search a 2D Matrix II

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

Given target = 5, return true.

Given target = 20, return false.

分析

从右上角开始, 比较target 和 matrix[i][j]的值。如果小于target, 则该行不可能有此数, 所以i++; 如果大于target, 则该列不可能有此数, 所以j—。遇到边界则表明该矩阵不含target.

代码

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原文: https://soulmachine.gitbooks.io/algorithm-essentials/content/cpp/search/search-a-2d-matrix-ii.html