README_EN.md

34. Find First and Last Position of Element in Sorted Array

中文文档

Description

Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.

If target is not found in the array, return [-1, -1].

You must write an algorithm with O(log n) runtime complexity.

 

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]

Example 3:

Input: nums = [], target = 0
Output: [-1,-1]

 

Constraints:

• 0 <= nums.length <= 105
• -109 <= nums[i] <= 109
• nums is a non-decreasing array.
• -109 <= target <= 109

Solutions

Binary search.

Template 1:

boolean check(int x) {}

int search(int left, int right) {
    while (left < right) {
        int mid = (left + right) >> 1;
        if (check(mid)) {
            right = mid;
        } else {
            left = mid + 1;
        }
    }
    return left;
}

Template 2:

boolean check(int x) {}

int search(int left, int right) {
    while (left < right) {
        int mid = (left + right + 1) >> 1;
        if (check(mid)) {
            left = mid;
        } else {
            right = mid - 1;
        }
    }
    return left;
}

Python3

class Solution:
    def searchRange(self, nums: List[int], target: int) -> List[int]:
        l = bisect_left(nums, target)
        r = bisect_left(nums, target + 1)
        return [-1, -1] if l == len(nums) or l >= r else [l, r - 1]

Java

class Solution {
    public int[] searchRange(int[] nums, int target) {
        int l = search(nums, target);
        int r = search(nums, target + 1);
        return l == nums.length || l >= r ? new int[]{-1, -1} : new int[]{l, r - 1};
    }

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

C++

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        int l = lower_bound(nums.begin(), nums.end(), target) - nums.begin();
        int r = lower_bound(nums.begin(), nums.end(), target + 1) - nums.begin();
        if (l == nums.size() || l >= r) return {-1, -1};
        return {l, r - 1};
    }
};

JavaScript

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var searchRange = function (nums, target) {
    function search(target) {
        let left = 0,
            right = nums.length;
        while (left < right) {
            const mid = (left + right) >> 1;
            if (nums[mid] >= target) {
                right = mid;
            } else {
                left = mid + 1;
            }
        }
        return left;
    }
    const l = search(target);
    const r = search(target + 1);
    return l == nums.length || l >= r ? [-1, -1] : [l, r - 1];
};

Go

func searchRange(nums []int, target int) []int {
	search := func(target int) int {
		left, right := 0, len(nums)
		for left < right {
			mid := (left + right) >> 1
			if nums[mid] >= target {
				right = mid
			} else {
				left = mid + 1
			}
		}
		return left
	}
	l, r := search(target), search(target+1)
	if l == len(nums) || l >= r {
		return []int{-1, -1}
	}
	return []int{l, r - 1}
}

Rust

impl Solution {
    pub fn search_range(nums: Vec<i32>, target: i32) -> Vec<i32> {
        let n = nums.len();
        let search = |target| {
            let mut left = 0;
            let mut right = n;
            while left < right {
                let mid = left + (right - left) / 2;
                if nums[mid] < target {
                    left = mid + 1;
                } else {
                    right = mid;
                }
            }
            left
        };
        let start = search(target);
        let end = search(target + 1) - 1;
        if start >= n || nums[start] != target {
            return vec![-1, -1];
        }
        vec![start as i32, end as i32]
    }
}

TypeScript

function searchRange(nums: number[], target: number): number[] {
    function search(target) {
        let left = 0,
            right = nums.length;
        while (left < right) {
            const mid = (left + right) >> 1;
            if (nums[mid] >= target) {
                right = mid;
            } else {
                left = mid + 1;
            }
        }
        return left;
    }
    const l = search(target);
    const r = search(target + 1);
    return l == nums.length || l >= r ? [-1, -1] : [l, r - 1];
}

function searchRange(nums: number[], target: number): number[] {
    const n = nums.length;
    const search = (target: number) => {
        let left = 0;
        let right = n;
        while (left < right) {
            const mid = (left + right) >>> 1;
            if (nums[mid] < target) {
                left = mid + 1;
            } else {
                right = mid;
            }
        }
        return left;
    };
    const start = search(target);
    const end = search(target + 1) - 1;
    if (nums[start] !== target) {
        return [-1, -1];
    }
    return [start, end];
}

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