JAVA刷题记录: 专题三 二分查找

704. 二分查找 - 力扣（LeetCode）

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

34. 在排序数组中查找元素的第一个和最后一个位置 - 力扣（LeetCode）

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

69. x 的平方根 - 力扣（LeetCode）

class Solution {
    public int mySqrt(int x) {
        long left = 1, right = x;
        if(x < 1) return 0;
        while(left < right) {
            long mid = left + (right - left + 1) / 2;
            if(mid * mid <= x) left = mid;
            else right = mid - 1; 
        }
        return (int)left;
    }
}

35. 搜索插入位置 - 力扣（LeetCode）

class Solution {
    public int searchInsert(int[] nums, int target) {
        int left = 0, right = nums.length - 1;
        while(left < right) {
            int mid = left + (right - left) / 2;
            if(nums[mid] < target) left = mid + 1;
            else right = mid;
        }
        if(nums[left] < target) left++;
        return left;
    }
}

852. 山脉数组的峰顶索引 - 力扣（LeetCode）

class Solution {
    public int peakIndexInMountainArray(int[] arr) {
        int left = 1, right = arr.length - 2;
        while(left < right) {
            int mid = left + (right - left + 1) / 2;
            if(arr[mid] > arr[mid -1]) left = mid;
            else right = mid - 1;
        }
        return left;
    }
}

162. 寻找峰值 - 力扣（LeetCode）

class Solution {
    public int findPeakElement(int[] nums) {
        int left = 0, right = nums.length - 1;
        while(left < right) {
            int mid = left + (right - left) / 2;
            if(nums[mid] < nums[mid + 1]) left = mid + 1;
            else right = mid;
        }
        return left;
    }
}

153. 寻找旋转排序数组中的最小值 - 力扣（LeetCode）

class Solution {
    public int findMin(int[] nums) {
        int left = 0, right = nums.length - 1;
        int x = nums[right];
        while(left < right) {
            int mid = left + (right - left) / 2;
            if(nums[mid] > x) left = mid + 1;
            else right = mid;
        }
        return nums[left];
    }
}

LCR 173. 点名 - 力扣（LeetCode）

class Solution {
    public int takeAttendance(int[] records) {
        int left = 0, right = records.length - 1;
        while(left < right) {
            int mid = left + (right - left) / 2;
            if(records[mid] == mid) left = mid + 1;
            else right = mid;
        }
        return left == records[left] ? left + 1 : left;
    }
}