LeetCode第二天&第三天

leetcode 第二天

2017年12月27日

4.（118）Pascal's Triangle

JAVA

class Solution {
    public List<List<Integer>> generate(int numRows) {
        List<List<Integer>> triangle = new ArrayList<List<Integer>>();
        //当numRows = 0 的情况
        if(numRows == 0) return triangle;
        //当numRows != 0 的情况
        triangle.add(new ArrayList<Integer>());
        triangle.get(0).add(1);
        
        for(int i = 1; i <numRows;i++){
            List<Integer> curRow = new ArrayList<Integer>();
            List<Integer> preRow = triangle.get(i-1);
            //first element
            curRow.add(1);
            
            for(int j = 0 ;j<preRow.size()-1;j++){
                curRow.add(preRow.get(j)+preRow.get(j+1));
            }
            curRow.add(1);
            triangle.add(curRow);        
        }
        return triangle;
    }
}

Python

def generate(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        triangle = []
        
        if numRows == 0:
            return triangle
        
        triangle.append([1])
        
        for i in range(1,numRows):
            curRow = []
            preRow = triangle[i-1]
            
            curRow.append(1)
            
            for j in range(len(preRow)-1):
                curRow.append(preRow[j]+preRow[j+1])
                
            curRow.append(1)
            triangle.append(curRow)
        return triangle

leetcode 第三天

2018年1月3日

5.（217）Contains Duplicate

JAVA

// T:O(nlogn)  S:O(1)
public boolean containsDuplicate(int[] nums) {
    Arrays.sort(nums);
    for (int i = 0; i < nums.length - 1; ++i) {
        if (nums[i] == nums[i + 1]) return true;
    }
    return false;
}

T:O(n)  S:O(n)
public boolean containsDuplicate(int[] nums) {
    Set<Integer> set = new HashSet<>(nums.length);
    for (int x: nums) {
        if (set.contains(x)) return true;
        set.add(x);
    }
    return false;
}

6.（717）1-bit and 2-bit Characters

JAVA

class Solution {
    public boolean isOneBitCharacter(int[] bits) {
        int i = 0;
        while (i<bits.length - 1){
            i += bits[i]+1;
        }
        return i == bits.length-1;
    }
}

class Solution {
    public boolean isOneBitCharacter(int[] bits) {
        int i = bits.length - 2;
        while (i >= 0 && bits[i] > 0) i--;
        return (bits.length - i) % 2 == 0;
    }
}

Python

class Solution(object):
    def isOneBitCharacter(self, bits):
        i = 0
        while i < len(bits) - 1:
            i += bits[i] + 1
        return i == len(bits) - 1

class Solution(object):
    def isOneBitCharacter(self, bits):
        parity = bits.pop()
        while bits and bits.pop(): parity ^= 1
        return parity == 0

7.（119）Pascal's Triangle II

Java

class Solution {
    public List<Integer> getRow(int rowIndex) {
        List<Integer> result = new ArrayList<Integer>();
        if(rowIndex < 0) return result;
        for(int i = 0 ;i <= rowIndex;i++){
            result.add(1);
            for(int j = i-1 ; j > 0 ; j--){
                result.set(j,result.get(j)+result.get(j-1));
            }
        }
        return result;
    }
}

8.（695）Max Area of Island

JAVA

递归

class Solution {
    int[][] grid;
    boolean[][] seen;
    public int maxAreaOfIsland(int[][] grid) {
        this.grid = grid;
        int result = 0;
        seen = new boolean[grid.length][grid[0].length];
        for(int r = 0;r<grid.length;r++)
            for(int c = 0 ;c<grid[0].length;c++)
                result = Math.max(result,area(r,c));
        return result;
    }
    
    public int area(int r,int c){
        if(r<0||r>=grid.length||c<0||c>=grid[0].length||seen[r][c]||grid[r][c]==0) return 0;
        seen[r][c] = true;
        return 1+area(r-1,c)+area(r,c-1)+area(r+1,c)+area(r,c+1);
    }
    
}

9.（26）Remove Duplicates from Sorted Array

JAVA

class Solution {
    public int removeDuplicates(int[] nums) {
        int newLength = 1;
        if(nums.length == 0) return 0;
        for(int i = 0;i<nums.length;i++)
            if(nums[newLength-1] != nums[i]){
                nums[newLength]= nums[i];
                newLength++;
            }
        return newLength;
    }
}

10.（27）Remove Element

JAVA

class Solution {
    public int removeElement(int[] nums, int val) {
        int newLength = 0;
        if(nums.length ==0) return newLength;
        for(int i = 0;i<nums.length;i++)
            if(nums[i]!=val)
                nums[newLength++] = nums[i];
        return newLength;
    }
}

11.（121）Best Time to Buy and Sell Stock

JAVA

class Solution {
    public int maxProfit(int[] prices) {
        int profit = 0;
        int min = Integer.MAX_VALUE;
        for(int i = 0;i<prices.length;i++){
            min = Math.min(prices[i],min);
            profit = Math.max(prices[i]-min,profit);
        }
        return profit;
    }
}

12.（122）Best Time to Buy and Sell Stock II

JAVA

class Solution {
    public int maxProfit(int[] prices) {
        int profit = 0;
        for(int i =0;i<prices.length-1;i++)
            if(prices[i+1]>prices[i])
                profit += prices[i+1]-prices[i];
        return profit; 
    }
}

13.（624）Maximum Distance in Arrays

Given m arrays, and each array is sorted in ascending order. Now you can pick up two integers from two different arrays (each array picks one) and calculate the distance. We define the distance between two integers a and b to be their absolute difference |a-b|. Your task is to find the maximum distance.

Example 1:

Input:
[[1,2,3],
[4,5],
[1,2,3]]
Output: 4
Explanation:
One way to reach the maximum distance 4 is to pick 1 in the first or third array and pick 5 in the second array.

Note:

1. Each given array will have at least 1 number. There will be at least two non-empty arrays.
2. The total number of the integers in all the m arrays will be in the range of [2, 10000].
3. The integers in the m arrays will be in the range of [-10000, 10000].

JAVA

public class Solution {  
    public int maxDistance(List<List<Integer>> arrays) {  
        int res = 0;  
        int min = arrays.get(0).get(0);  
        int max = arrays.get(0).get(arrays.get(0).size() - 1);  
        for (int i = 1; i < arrays.size(); i++) {  
            List<Integer> array = arrays.get(i);  
            res = Math.max(Math.abs(min - array.get(array.size() - 1)), Math.max(Math.abs(array.get(0) - max), res));  
            min = Math.min(min, array.get(0));  
            max = Math.max(max, array.get(array.size() - 1));  
        }  
        return res;  
    }  
}  

14.（35）Search Insert Position

JAVA

class Solution {
    public int searchInsert(int[] nums, int target) {
        for(int i =0;i<nums.length;i++){
            if(nums[i] == target)
                return i;
            if(nums[i]>target)
                return i;
        }
        return nums.length;
    }
}