# 二分查找左边界
实现原理: 传入的是一个有序的数组, 左右递减, 取中间下标进行匹配, 如果中值小于目标值, 左下标向右移动一位, 小于则右下标等于中下标, 缩小搜索边界
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/**
* 二分查找左边界
* @param {number[]} nums
* @param {number} target
* @returns number
*/
const binarySearchLeftBound = (nums, target) => {
// let left = 0,
// right = nums.length
// while(left < right) {
// const mid = left + ((right - left) >> 1)
// if (nums[mid] < target) {
// left = mid + 1
// } else {
// right = mid
// }
// }
// return nums[left] === target ? left : -1
// --- TODO: Test case ---
let left = 0,
right = nums.length - 1
while(left <= right) {
const mid = left + ((right - left) >> 1)
if (nums[mid] < target) {
left = mid + 1
} else {
right = mid - 1
}
}
return nums[left] === target ? left : -1
}
// ---------- Test ---------
const nums = [1, 2, 3, 4, 5, 5, 5, 5, 5, 5, 6];
const target = 5
console.log(binarySearchLeftBound(nums, target))
// 4
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