剑指offer——面试题3：二维数组中的查找

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看《剑指offer》中的解释更加容易理解！！！

Python

class Solution:
    def findTargetIn2DPlants(self, plants: List[List[int]], target: int) -> bool:
        if len(plants) == 0 or len(plants[0]) == 0:
            return False
        m, n = len(plants), len(plants[0])
        i, j = 0, n-1
        while i < m and j >= 0:
            if target == plants[i][j]:
                return True
            elif target < plants[i][j]:
                j -= 1
            else:
                i += 1
        return False

Java

class Solution {
    public boolean findTargetIn2DPlants(int[][] plants, int target) {
        if (plants.length == 0 || plants[0].length == 0) {
            return false;
        }
        int i = 0, j = plants[0].length - 1;
        while (i >= 0 
                && j >=0
                && i < plants.length 
                && j < plants[0].length) {
            if (plants[i][j] == target) {
                return true;
            } else if (plants[i][j] > target) {
                --j;
            } else {
                ++i;
            }
        }

        return false;
    }
}

1.笨蛋方法

复杂度为$O(n^2)$

class Solution {
public:
    bool Find(int target, vector<vector<int> > array) {
        for(int i=0;i<array.size();i++){
            for(int j=0;j<array[0].size();j++){
                if(array[i][j]==target)
                    return true;
            }
        }
        return false;
    }
};

2.稍微聪明点的解法

算法是《剑指offer》上的思路，自己用c++实现，并在牛客网上AC。
Solution1：初始化为右上角的点

class Solution {
public:
    bool Find(int target, vector<vector<int> > array) {
        int row = array.size(),col=array[0].size();//有row行，col列
        if(row == 0 || col == 0) return false;
        int i = 0,j = col-1;//初始化为第1行，最后一列
        while(i <= row-1 && j >= 0){
            if(array[i][j] == target)
                return true;
            else if(array[i][j] < target)
                i++;
            else if(array[i][j] > target)
                j--;
        }
        return false;
    }
};

Solution2：初始化为左下角的点

class Solution {
public:
    bool Find(int target, vector<vector<int> > array) {
        int row = array.size(),col=array[0].size();//有row行，col列
        if(row == 0 || col == 0) return false;
        int i = row-1,j = 0;//初始化为最后1行，第1列
        while(i >=0 && j <= col-1){
            if(array[i][j] == target)
                return true;
            else if(array[i][j] > target)
                i--;
            else if(array[i][j] < target)
                j++;
        }
        return false;
    }
};

20190831重做
C++版

class Solution {
public:
    bool Find(int target, vector<vector<int> > array) {
        if (!array.size() || !array[0].size())
            return false;
        int i = 0, j = array[0].size() - 1;
        while (i <= array.size() - 1 && j >= 0) {
            if (array[i][j] == target) {
                return true;
            } else if (array[i][j] < target){
                i++;
            } else {
                j--;
            }
        }
        return false;
    }
};

Java版

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