Two Pointers — Opposite Ends

Key Signals & Indicators

• Sorted input array, string, or matrix
• Searching for pairs that satisfy a condition (sum, products)
• Requires constant auxiliary space O(1)

// C++ Two Pointers Opposite Ends Template
#include <vector>

std::pair<int, int> oppositePointers(const std::vector<int>& arr, int target) {
    int left = 0;
    int right = arr.size() - 1;
    
    while (left < right) {
        int sum = arr[left] + arr[right];
        if (sum == target) {
            return {left, right};
        } else if (sum < target) {
            left++; // Move left pointer inward
        } else {
            right--; // Move right pointer inward
        }
    }
    return {-1, -1};
}