【Hot100】LeetCode—34. 在排序数组中查找元素的第一个和最后一个位置

• 原题链接：34. 在排序数组中查找元素的第一个和最后一个位置

1- 思路

二分 - 左侧二分 + 右侧二分

• 右区间二分 ——> 找首次出现的位置 ——>nums[mid] >= target
• 左区间二分 ——> 找最后一次出现的位置 ——> **nums**[mid] <= target

2- 实现

⭐34. 在排序数组中查找元素的第一个和最后一个位置——题解思路

class Solution {
    public int[] searchRange(int[] nums, int target) {
        int[] res = new int[2];
        Arrays.fill(res,-1);
        if(nums.length == 0 || nums==null){
            return res;
        }
        int left = 0;
        int right = nums.length-1;
        while(left<right){
            int mid = (left+right)/2;
            if(nums[mid] >= target){
                right = mid;
            }else{
                left = mid+1;
            }
        }
        if(nums[left]==target){
            res[0] = left;
        }
        left = 0;
        right = nums.length-1;
        while(left<right){
            int mid = (left+right+1)/2;
            if(nums[mid] <= target){
                left = mid;
            }else{
                right = mid-1;
            }
        }
        if(nums[left]==target){
            res[1] = left;
        }
        return res;
    }
}

3- ACM 实现

public class findFirstAndLast {

    public static int[] finFAndL(int[] nums,int target){
        int[] res = new int[2];
        Arrays.fill(res,-1);
        int left = 0;
        int right = nums.length-1;
        while(left<right){
            int mid = (left+right)/2;
            if(nums[mid] >= target){
                right = mid;
            }else{
                left = mid+1;
            }
        }
        
        if(res[left]==target){
            res[0] = left;
        }
        left = 0;
        right = nums.length-1;
        while(left<right){
            int mid = (left+right+1)/2;
            if(nums[mid] <= target){
                left = mid;
            }else{
                right = mid-1;
            }
        }
        if(res[left]==target){
            res[1] = left;
        }
        return res;
    }


    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String input = sc.nextLine();
        input = input.substring(1,input.length()-1);
        String[] parts = input.split(",");
        int[] nums = new int[parts.length];
        for(int i = 0 ; i < nums.length;i++){
            nums[i] = Integer.parseInt(parts[i]);
        }
        System.out.println("输入target");
        int target = sc.nextInt();

        int[] res = finFAndL(nums,target);
        System.out.println("结果是"+res[0]+" "+res[1]);
    }
}