合并有序数组，不使用新数组

[Twlig]

function mergeArr(arr1, arr2) {
    let n1 = arr1.length
    let n2 = arr2.length
    let indexArr1 = 0
    for(let i = 0; i < n2; i++) {
        while(arr1[indexArr1] < arr2[i] && indexArr1 < n1) {
            indexArr1++
        }
        arr1.splice(indexArr1, 0, arr2[i])
        indexArr1++
    }
    return arr1
}
let arr1 = [1, 4, 5]
let arr2 = [2, 3, 4]
console.log(mergeArr(arr1, arr2))