Leetcode array class

704 topic ： Two points search

Given a n The elements are ordered （ Ascending ） integer array nums And a target value target , Write a function search nums Medium target, If the target value has a return subscript , Otherwise return to -1.

Two points search
1） Conditions ： The elements are in order , No repeating elements
2） The process ： Suppose the elements in the table are arranged in ascending order , Compare the middle position element with the lookup element , equal , Then the search is successful ; Otherwise, use the middle position record to divide the table into front 、 Last two sub tables , If the key of the intermediate location record is greater than the search key , Then look up the previous sub table , Otherwise, look up the next sub table .

class Solution(object):
    def search(self, nums, target):
        left,right=0,len(nums)-1
        while left<=right:
            middle=(right-left)//2
            if target>nums[middle]:
                left=middle+1
            elif target<nums[middle]:
                right=middle-1
            else:
                return middle
        return -1

27 topic ： Remove elements

Give you an array nums And a value val, You need In situ Remove all values equal to val The elements of , And return the new length of the array after removal .

Double finger needling （ Fast and slow pointer method ）
1） Definition ： The fast pointer points to the element currently being processed , The slow pointer points to the next position to be assigned
2） Use occasion ： A lot of research 、 Linked list 、 Interview questions for string and other operations , They all use double finger acupuncture .

class Solution(object):
    def removeElement(self, nums, val):
        left=0
        for right in range(0,len(nums)):
            # If they are not equal, they will be overwritten on the original array 
            if nums[right]!=val:
                nums[left]=nums[right]
                left+=1
        return left