标签：出现 ++ solution value array exit and int fir
Given an array of integers nums sorted in ascending order, find the starting and ending position of a given target value.
Your algorithm‘s runtime complexity must be in the order of O(log n).
If the target is not found in the array, return [-1, -1].
Example 1:
Input: nums = [5,7,7,8,8,10], target = 8
Output: [3,4]
Example 2:
Input: nums = [5,7,7,8,8,10], target = 6
Output: [-1,-1]
先使用二分查找找到和taget相等的起始位置的元素，然后在这个位置向两边扩散找到值相同的范围。
class Solution { public: vector<int> searchRange(vector<int>& nums, int target) { vector<int> res(2,-1); if(nums.size() == 0) return res; int cau = dichotomy(nums,target); if(cau == -1) return res; else{ int i = cau,j = cau; cout<<cau<<endl; while((i>=0 && nums[i] == target) || (j<=nums.size()-1 && nums[j] == target)){ if(i>=0 && nums[i] == target){ res[0] = i; cout<<i<<endl; i--; } if(j<=nums.size()-1 && nums[j] == target){ res[1] = j; cout<<j<<endl; j++; } } } return res; } int dichotomy(vector<int>& nums, int target){ int low = 0,int high = nums.size() - 1; while(low < high){ int mid = (low + high + 1) / 2; if(nums[mid] == target) return mid; if(nums[mid] < target) low = mid + 1; else high = mid - 1; } return -1; } };
先根据上述的二分查找，找到起始位置的元素，然后从low开始继续使用一次二分查找找到target+1的位置，然后返回这个位置it - 1，从而找到起始和终止的范围。
class Solution { public: vector<int> searchRange(vector<int>& nums, int target) { vector<int> res(2,-1); if(nums.size() == 0) return res; int low = dichotomy(nums,target,0); //找起始元素 cout<<low<<endl; if(low == nums.size() || nums[low] != target) //可能出现到数组结尾还是target比low处元素大，low=nums.size return res; else{ res[0] = low; res[1] = dichotomy(nums,target+1,low) - 1; //找结尾元素 } return res; } int dichotomy(vector<int>& nums, int target, int low){ int high = nums.size(); //核心 while(low < high){ int mid = (low + high ) / 2; if(nums[mid] < target) low = mid + 1; else high = mid; } return low; } };
【LeetCode】【找元素】Find First and Last Position of Element in Sorted Array
标签：出现 ++ solution value array exit and int fir
原文地址：https://www.cnblogs.com/ygh1229/p/9726966.html
