【练习】二分查找

1、704

（1）题目描述

（2）代码实现

package com.hh.practice.leetcode.array.demo_02;public class BinarySearch_704 {public int search(int[] nums, int target) {int i= 0,j = nums.length -1;while (i <= j){int mid = (i+j) >>> 1;if (target < nums[mid]){j = mid - 1;} else if (nums[mid] < target) {i = mid + 1;}else {return mid;}}return -1;}//方式一
//    public int search(int[] nums, int target) {
//        for(int i = 0; i < nums.length; i++){
//            if(target == nums[i]){
//               return i;
//            }
//        }
//        return -1;
//    }
}

2、35

（1）题目描述

（2）代码实现

package com.hh.practice.leetcode.array.demo_02;public class BinarySearch_35 {//方式二public static int searchInsert(int[] arr, int key) {int i = 0;int j = arr.length - 1;while (i <= j) {int mid = (i + j) >>> 1;if (key <= arr[mid]) {j = mid - 1;} else{i = mid + 1;}}return i;}//方式一
//    public int searchInsert(int[] nums, int target) {
//        int low = 0;
//        int high = nums.length - 1;
//
//        while (low <= high) {
//            int mid = (low + high) >>> 1;
//            int midVal = nums[mid];
//
//            if (midVal < target)
//                low = mid + 1;
//            else if (midVal > target)
//                high = mid - 1;
//            else
//                return mid; // target found
//        }
//        //没找到就返回插入点，
//        return low;  // target not found.
//    }
}

3、34

（1）题目描述‘

（2）代码实现

package com.hh.practice.leetcode.array.demo_02;public class BinarySearch_34 {public int[] searchRange(int[] nums, int target) {int[] arr = new int[2];arr[0] = binaryLeft(nums,target);if (arr[0] == -1){arr[1] = -1;} else {arr[1] = binaryRight(nums, target);}return arr;}/*返回最靠左的元素索引*/public int binaryLeft(int[] arr, int key) {int i = 0;int j = arr.length - 1;int candidate = -1;while (i <= j) {int mid = (i + j) >>> 1;if (key < arr[mid]) {j = mid - 1;} else if (key > arr[mid]) {i = mid + 1;} else {candidate = mid;j = mid -1;}}return candidate;}/*返回最靠右的元素索引*/public int binaryRight(int[] arr, int key) {int i = 0;int j = arr.length - 1;int candidate = -1;while (i <= j) {int mid = (i + j) >>> 1;if (key < arr[mid]) {j = mid - 1;} else if (key > arr[mid]) {i = mid + 1;} else {candidate = mid;i = mid +1;}}return candidate;}
}

 

 

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