《LeetCode力扣练习》代码随想录——数组（二分查找---Java）

《LeetCode力扣练习》代码随想录——数组（二分查找—Java）

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刷题思路来源于 代码随想录

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704. 二分查找

• 左闭右闭——[x,y]

  class Solution {
      public int search(int[] nums, int target) {
  
        if(nums.length==0||nums==null){
          
          return -1;
  
        }
  
        int left=0;
        int right=nums.length-1;
  
        while(left<=right){
  
          int middle=left+(right-left)/2;
  
          if(nums[middle]<target){
  
            left=middle+1;
  
          }else if(nums[middle]>target){
  
            right=middle-1;
  
          }else{
  
            return middle;
  
          }
  
        }
  
        return -1;
  
      }
  }
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• 左闭右开——[x,y)

  class Solution {
      public int search(int[] nums, int target) {
  
          if(nums.length==0||nums==null){
              return -1;
          }
  
          int left=0;
          int right=nums.length;
  
          while(left<right){
  
              int middle=left+(right-left)/2;
  
              if(nums[middle]>target){
                  right=middle;
              }else if(nums[middle]<target){
                  left=middle+1;
              }else{
                  return middle;
              }
  
          }
  
          return -1;
  
      }
  }
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35. 搜索插入位置

• 左闭右闭——[x,y]

  class Solution {
      public int searchInsert(int[] nums, int target) {
  
        if(nums.length==0||nums==null){
          return -1;
        }
  
        int n=nums.length;
  
        if(target<nums[0]){
          return 0;
        }
  
        if(target>nums[n-1]){
          return n;
        }
  
        int left=0;
        int right=n-1;
  
        while(left<=right){
  
          int middle=left+(right-left)/2;
  
          if(nums[middle]<target){
            left=middle+1;
          }else if(nums[middle]>target){
            right=middle-1;
          }else{
            return middle;
          }
  
        }
  
        // 其实这个也可以
        // return left;
        return right+1;
  
      }
  }
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34. 在排序数组中查找元素的第一个和最后一个位置

• 左闭右闭——[x,y]

  class Solution {
      public int[] searchRange(int[] nums, int target) {
  
          if(nums==null||nums.length==0){
              return new int[]{-1,-1};
          }
  
          if(target<nums[0]||target>nums[nums.length-1]){
              return new int[]{-1,-1};
          }
  
          int left=findLeft(nums,target);
          int right=findRight(nums,target);
  
          if(left==-2||right==-2){
              return new int[]{-1,-1};
          }
  
          return new int[]{left+1,right-1};
  
      }
  
      private int findLeft(int[] nums, int target){
  
          int result=-2;
          int left=0;
          int right=nums.length-1;
  
          while(left<=right){
  
              int middle=left+(right-left)/2;
  
              if(nums[middle]>target){
  
                  right=middle-1;
  
              }else if(nums[middle]<target){
  
                  left=middle+1;
  
              }else{
                  
                  right=middle-1;
                  result=right;
  
              }
  
          }
  
          return result;
  
      }
  
      private int findRight(int[] nums, int target){
  
          int result=-2;
          int left=0;
          int right=nums.length-1;
  
          while(left<=right){
  
              int middle=left+(right-left)/2;
  
              if(nums[middle]<target){
  
                  left=middle+1;
  
              }else if(nums[middle]>target){
  
                  right=middle-1;
  
              }else{
  
                  left=middle+1;
                  result=left;
  
              }
  
          }
  
          return result;
  
      }
  }
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69. x 的平方根

• 左闭右闭——[x,y]

  class Solution {
      public int mySqrt(int x) {
  
          if(x==0||x==1){
              return x;
          }
  
          int left =0;
          int right=x/2+1;
  
          while(left<=right){
  
              int middle=left+(right-left)/2;
              long result=(long)middle*middle;
  
              if(result>x){
                  right=middle-1;
              }else if(result<x){
                  left=middle+1;
              }else{
                  return middle;
              }
  
          }
  
          return right;
  
      }
  }
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367. 有效的完全平方数

• 左闭右闭——[x,y]

  class Solution {
      public boolean isPerfectSquare(int num) {
  
          if(num==0||num==1){
              return true;
          }
  
          int left=1;
          int right=num/2+1;
  
          while(left<=right){
  
              int middle=left+(right-left)/2;
              long result=(long)middle*middle;
  
              if(result<num){
                  left=middle+1;
              }else if(result>num){
                  right=middle-1;
              }else{
                  return true;
              }
  
          }
  
          return false;
  
      }
  }
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