First Occurrence - Binary Search / Sorted Array

Problems
21

Solution in Go:
func findFirstOccurrence(arr []int, target int) int {
left := 0
right := len(arr) - 1
idx := -1

for left <= right {
    mid := left + (right - left) / 2
    if feasible(arr, mid, target) {
        idx = mid
    }
    if arr[mid] < target {
        left = mid + 1
    } else {
        right = mid - 1
        
    }
}
return idx

}

22

2nd post try, now with func feasible that is only a check
func feasible(arr[]int, idx int, target int) bool {
if arr[idx] == target {
return true
}
return false
}

func findFirstOccurrence(arr []int, target int) int {
left := 0
right := len(arr) - 1
idx := -1

for left <= right {
    mid := left + (right - left) / 2
    if feasible(arr, mid, target) {
        idx = mid
    }
    if arr[mid] < target {
        left = mid + 1
    } else {
        right = mid - 1
        
    }
}
return idx

}

23

You can use the classic solution with a little bit of an extra test at the end:

    public static int findFirstOccurrence(List<Integer> arr, int target) {

        int left = 0 ;
        int right = arr.size() - 1;
        int result = -1;

        while (left <= right) {
            int mid = left + (right - left) / 2;

            if (arr.get(mid) >= target) {
                result = mid;
                right = mid - 1;
            }
            else
                left = mid + 1;
        }
        return result != -1 && arr.get(result) == target ? result : -1;
    }
24

Can solve without using extra variable

function firstNotSmaller(arr, target) {
let left = 0,
right = arr.length - 1,
firstIndex = -1
while(left <= right){
let mid = left + Math.floor((right - left) / 2);
if(arr[mid] >= target){
right = mid-1;
}else{
left = mid+1;
}
}
return left
}

25

It looks like the template for this (shown by the template button under the input box for the problem) is linked to the backtracking templates which doesn’t seem correct here