Day8-String01

344. Reverse String

Node:

• Two pointers
• Reverse inplace
  The reverse() method of Array instances reverses an array in place and returns the reference to the same array

Time Complexity && Space Complexity

• Time Complexity: O(n)
• Space Complexity: O(1)

var reverseString = function(s) {
    let start = 0;
    let end = s.length - 1;
    while(start <= end){
        let temp = s[start];
        s[start] = s[end];
        s[end] = temp;
        start++;
        end--;
    }
    return s;
};

541. Reverse String II

Node:

• can’t change the string’s char by string1[0] = "c", it doesn’t work

  • In JavaScript, strings are immutable, which means once a string is created, its characters cannot be changed directly.

    • String: let str = "hello"; str = str + " world"; (This creates a new string rather than modifying the original str).
    • Numbers: Numbers are also immutable. Any operation on a number returns a new number rather than modifying the original value.
    • Booleans: true and false are immutable.
    • null and undefined: These are immutable by nature, as they represent the absence of value.
    • Symbols: Introduced in ES6, symbols are unique and immutable. Once created, a symbol’s value cannot be changed.
      (All primitive type are immutable, You cannot change a primitive’s value. Any operation that appears to change a primitive actually creates a new primitive.)

  • Convert to a array and then change it by arr[0] = "c"

Time Complexity && Space Complexity

• Time Complexity: O(n)
• Space Complexity: O(1)

var reverseStr = function(s, k) {
    let start = 0;
    let end = start + k-1;
    const arr = s.split("");
    for(let i = 0; i < s.length; i+=2*k){
        const start = i;
        const end = start + k - 1;
        reverse(arr, start, end < arr.length ? end : arr.length);
    }
    return arr.join("");
};

var reverse = function(arr, start, end){
    while(start <= end){
        let temp = arr[start];
        arr[start] = arr[end];
        arr[end] = temp;
        start++;
        end--;
    }
}