Binary Search Universal Formula
Binary Search(Universal Formula)
Pattern 1: Basic template
/* Pattern 1: Search for any element that meets the condition, tighten the boundary to the right-side */
public int binarySearchPattern1(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 indicates not found
return -1;
}
Pattern 2: Find the first location equal to the target
/* Pattern 2: Search for the leftmost element that meets the condition, tighten left-side boundary */
public int binarySearchPattern2(int[] nums, int target) {
int left = 0, right = nums.length;
while (left < right) {
int mid = left + (right - left) / 2;
if (nums[mid] < target) {
left = mid + 1;
} else {
right = mid;
}
}
return left;
}
Pattern 3: Find the last position equal to the target
/* Pattern 3: Search for the rightmost element that meets the condition, result just meets the conditions */
public int binarySearchPattern3(int[] nums, int target) {
int left = 0, right = nums.length;
while (left < right) {
int mid = left + (right - left) / 2;
if (nums[mid] <= target) {
left = mid + 1;
} else {
right = mid;
}
}
return right - 1;
}
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