leedcode算法入门：二分法查找

目录

什么是二分查找 

704.二分查找

 278.第一个错误的版本

35.插入搜索位置 

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什么是二分查找 

二分法查找原理

704.二分查找

题目描述：

代码：

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

        return -1;
    }
}

 278.第一个错误的版本

题目描述：

代码：

 

/* The isBadVersion API is defined in the parent class VersionControl.
      boolean isBadVersion(int version); */

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
        int low = 1;
        int mid = (n+1)/2;
        int high = n ;
        while (low <high){
            mid = low+(high-low)/2;
            if ( !isBadVersion(mid)){
                low = mid +1 ;
            }else{
                high = mid ;
            }
        }
        return low;
    }
}

35.插入搜索位置 

题目描述：

代码：

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