刷题|剑指 Offer 53 - I. 在排序数组中查找数字 I_JavaScript

题目描述

剑指 Offer 53 - I. 在排序数组中查找数字 I

解题思路

方法1：循环法

方法2： 二分法

注意：题目中说数组nums是排序数组
感谢大佬提供的思路：剑指Offer——在排序数组中查找数字I（JS实现）

代码实现

方法1：循环法

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number}
 */
var search = function(nums, target) {
    if (!nums.includes(target)) return 0

    let m = new Map();
    for (let i of nums) {
        if (!m.has(i)) {
            m.set(i,1);
        } else {
            let count = m.get(i);
            m.set(i, count+1);
        };
    };

    return m.get(target);

};

方法2：二分法

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number}
 */
var search = function (nums, target) {
    if (!nums.includes(target) || !nums.length) return 0;
    let left = 0, right = nums.length - 1;
    let mid = Math.floor((left + right) / 2);
    while (nums[mid] !== target) {
        if (left === right) return 0;
        if (nums[mid] < target) {
            left = mid + 1;
            if (left === nums.length) return 0;
            mid = Math.floor((left + right) / 2);
            continue;
        }
        if (nums[mid] > target) {
            right = mid - 1;
            if (right < 0) return 0;
            mid = Math.floor((left + right) / 2);
            continue;
        }
    }
    let flag1 = mid;
    let flag2 = mid;
    let left_border,right_border;
    while (nums[flag1-1] === target) {
        flag1--;
    }
    left_border = flag1;
    while (nums[flag2+1] === target) {
        flag2++;
    }
    right_border = flag2;
    return right_border - left_border + 1;
};