1、返回查找值的隨機索引
- 搜索區間是 [left, right] 的左閉右閉寫法
int binary_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) {
left = mid + 1;
} else if (nums[mid] > target) {
right = mid - 1;
} else if(nums[mid] == target) {
return mid;
}
}
return -1;
}
- 搜索區間是 [left, right) 的左閉右開寫法
def binary_search(list_a, target):
left = 0
right = len(list_a)
while left < right:
mid = (left + right) // 2
if list_a[mid] == target:
return mid
elif list_a[mid] < target:
left = mid + 1
elif list_a[mid] > target:
right = mid
return -1
2、返回查找值的左邊界索引
- 搜索區間是 [left, right] 的左閉右閉寫法
int left_bound(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 if (nums[mid] > target) {
right = mid - 1;
} else if (nums[mid] == target) {
right = mid - 1;
}
}
if (left == nums.length) return -1;
return nums[left] == target ? left : -1;
}
- 搜索區間是 [left, right) 的左閉右開寫法
int left_bound(int[] nums, int target) {
if (nums.length == 0) return -1;
int left = 0;
int right = nums.length;
while (left < right) {
int mid = (left + right) / 2;
if (nums[mid] == target) {
right = mid;
} else if (nums[mid] < target) {
left = mid + 1;
} else if (nums[mid] > target) {
right = mid;
}
}
if (left == nums.length) return -1;
return nums[left] == target ? left : -1;
}
3、返回查找值的右邊界索引
- 搜索區間是 [left, right] 的左閉右閉寫法
int right_bound(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 if (nums[mid] > target) {
right = mid - 1;
} else if (nums[mid] == target) {
left = mid + 1;
}
}
return nums[left-1] == target ? left-1 : -1;
}
- 搜索區間是 [left, right) 的左閉右開寫法
int right_bound(int[] nums, int target) {
if (nums.length == 0) return -1;
int left = 0, right = nums.length;
while (left < right) {
int mid = (left + right) / 2;
if (nums[mid] == target) {
left = mid + 1;
} else if (nums[mid] < target) {
left = mid + 1;
} else if (nums[mid] > target) {
right = mid;
}
}
return nums[left-1] == target ? left-1 : -1;
}
4、總結一下兩種寫法的區別
- while裏面的條件用 ‘<’ 還是 '<= '。
- right的更新用 ‘mid - 1’ 還是 ‘mid’。
- 對於查找左邊界來說無論哪種寫法都需要判斷索引溢出,就算你用right來返回最後值,也要判斷right是否小於0。
- 返回隨機索引和右邊界索引不用判斷索引溢出。
5、鳴謝
參考博客在此