leetCode 74.Search a 2D Matrix(搜尋二維矩陣) 解題思路和方法

標籤：leetcode

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：此題還是比較簡單的，主要是用兩個二分法，才對第一列使用，再對特定的行使用。

具體代碼如下：

public class Solution {    public boolean searchMatrix(int[][] m, int target) {        //兩個二分搜尋        //先搜尋第一列，找到確定的行，然後再搜尋行        int i = 0;        int j = m.length-1;        int mid = 0;        //搜尋第一列        while(i <= j){            mid = (i + j)/2;            if(m[mid][0] == target){                return true;            }else if(m[mid][0] < target){                i = mid + 1;            }else{                j = mid - 1;            }        }        if(m[mid][0] > target){            if(mid == 0){                return false;            }            mid--;//mid-1        }        //搜尋mid行        i = 0;        j = m[0].length -1;        int k = mid;        //搜尋到了返回true        while(i <= j){            mid = (i + j)/2;            if(m[k][mid] == target){                return true;            }else if(m[k][mid] < target){                i = mid + 1;            }else{                j = mid - 1;            }        }        //沒有搜尋到，返回false        return false;    }}

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leetCode 74.Search a 2D Matrix(搜尋二維矩陣) 解題思路和方法