Opposite Direction Pointers Template
In this Template, pointers start from opposite ends of the array (one at the beginning, the other at the end).
The pointers move towards each other based on certain conditions until they meet.
Common use cases: checking for palindromes, two-sum in sorted arrays, and merging intervals.
Basic Template Structure: –
Java
int left = 0;
int right = arr.length - 1;
while (left < right) {
//code
left++;
right--;
}Scenario 1: – Target specific equality check.
If we have a target in our problem and our elemnts sum is equal to target.
Java
int left = 0;
int right = arr.length - 1;
while (left < right) {
//code
if (currentSum == target) {
left++;
right--;
}
}Scenario 2: – Less than check.
If we have a target in our problem and our elemnts sum is less than target.
Java
int left = 0;
int right = arr.length - 1;
while (left < right) {
//code
if (currentSum < target) {
left++;
}
}Scenario 3: – Greater than check.
If we have a target in our problem and our elemnts sum is greater than target.
Java
int left = 0;
int right = arr.length - 1;
while (left < right) {
//code
if (currentSum > target) {
right--;
}
}Final Template: – combined all the scenarios into a single structure with generic parameters
Java
int left = 0;
int right = arr.length - 1;
while (left < right) {
//code
if (param1 == param2) {
// code
left++;
right--;
} else if (param1 < param2) {
left++;
} else {
right--;
}
}