Finally know the difference between the two templates! [hand drawn cartoon] illustration of finding the first and last position of elements in sorted array (leetcode 34)

I'm Guan Xiaoliang 2020-11-13 05:30:31
finally know difference templates hand


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The illustration LeetCode Brush question plan

1、 Write it at the front

Hand drawn cartoon series officially launched !!!“ The illustration LeetCode Brush question plan ” coming !!!

Today is issue 16 , Strive for one issue a day , Up to two days , You are welcome to supervise me ...
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Template summary :

an issue rooted in history :
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What is the difference between the two templates ???

take it easy , Let's look at today's question .
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2、 subject

First look at the topic ,
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Normal binary search , There's a limit to repetition , In addition, the head and tail positions of repeating elements are required .

And then inadvertently , I found the secret .
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3、 Text

Let's see what the secret is ?

The first sequence is 5、7、7、8、10,target=7, Search by template 1 / 2 .

int left=0;
int right=nums.size()-1;
while(left<right){

int mid=left+right>>1;
if(nums[mid]>=target){

right=mid;
}
else{

left=mid+1;
}
}
return left;

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You can see , It returns the value on the left ,mid It's going down ,right It's also , therefore ~

And template two ?

int left=0;
int right=nums.size()-1;
while(left<right){

int mid=(left+right+1)>>1;
if(nums[mid]<=target){

left=mid;
}
else{

right=mid-1;
}
}
return right;

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You can see , It returns the value on the right ,mid It's going up ,left It's also , therefore ~

The last returned value is written as left perhaps right No problem ! because while The end condition of is left and right equal .
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4、 Code

class Solution {

public:
vector<int> searchRange(vector<int>& nums, int target) {

if(nums.empty()) return {
-1,-1};
int left=0;
int right=nums.size()-1;
while(left<right){

int mid=(left+right)>>1;
if(nums[mid]>=target){

right=mid;
}
else{

left=mid+1;
}
}
if(nums[left]!=target) return {
-1,-1};
int start=left;
left=0;
right=nums.size()-1;
while(left<right){

int mid=(left+right+1)>>1;
if(nums[mid]<=target){

left=mid;
}
else{

right=mid-1;
}
}
if(nums[left]!=target) return {
-1,-1};
int end=right;
return {
start,end};
}
};

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If I have the honor to help you , Please order one for me 【 Fabulous 】, Give me one 【 Focus on 】! If you can bring along 【 Comment on 】 Give me a piece of encouragement , I would be grateful .

If you want more resources , Welcome to your attention @ I'm Guan Xiaoliang , Obsessive compulsive disorder MAX~

版权声明
本文为[I'm Guan Xiaoliang]所创,转载请带上原文链接,感谢

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