leetcode 34 在排序数组中查找元素的第一个和最后一个位置

简介

暴力, 不过推荐官方的二分查找

code

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        bool check = false;
        int indexS=-1, indexE = -1;
        for(int i=0; i<nums.size(); i++){
            
            if(nums[i] == target && !check){
                indexS = i;
                check = true;
            }else if(check && nums[i] > target){
                indexE = i - 1;
                check = false;
                return {indexS, indexE};
            }
            if(nums[i] > target && !check) return {-1, -1};
        }
        if(check && indexE == -1) {
            indexE = nums.size() - 1;
        }
        return {indexS, indexE};
    }
};

class Solution {
    public int[] searchRange(int[] nums, int target) {
        int len = nums.length;
        if(len == 0) {
            return new int[]{-1, -1};
        }

        int firstPosition = findFirstPosition(nums, target);
        if(firstPosition == -1){
            return new int[] {-1, -1};
        }

        int lastPosition = findLastPosition(nums, target);
        return new int[]{firstPosition, lastPosition};
    }

    private int findLastPosition(int[] nums, int target) {
        int left = 0;
        int right = nums.length -1;
        while(left < right) {
            int mid = (left + right + 1) >>> 1; // 让其更靠近右边界
            if(nums[mid] < target) {
                left = mid + 1;
            } else if(nums[mid] == target) {
                left = mid;
            } else{
                right = mid - 1;
            }
        }
        return left;
    }

    private int findFirstPosition(int[] nums, int target) {
        int left = 0;
        int right = nums.length -1;
        while(left < right) {
            int mid = (left + right) >>> 1;
            if(nums[mid] < target) {
                left = mid + 1;
            } else if(nums[mid] == target) {
                right = mid;
            } else{
                right = mid - 1;
            }
        }
        if(nums[left] == target){
            return left;
        }
        return -1;
    }
}