數組上的隨機值

Question

我想在數組上生成一個隨機值。 但是每次單擊時，數組都會獲得一個新值，所以我不想獲得一個已經在數組上具有值的隨機值。 簡而言之，我需要隨機獲取數組的空值。

這是代碼的一小部分。 我的數組上有9個值，一開始它們都是空的。

var gameCase = ['', '', '', '', '', '', '', '', ''];
var randomValue = gameCase[VALUE_EMPTY*][Math.round(Math.random()*gameCase.length)];

*這是我不知道該怎么做的部分。

Answer 1

有幾種方法可以解決此問題：

方法1：繼續生成隨機索引，直到它指向一個空值

var gameCase = ['', '', '', '', '', '', '', '', ''];
var randomIndex = Math.round(Math.random()*gameCase.length) % emptyCases.length;
var randomValue = gameCase[randomIndex];
// while we haven't found the empty value
while (randomValue !== '') {
    // keep on looking
    randomIndex = Math.round(Math.random()*gameCase.length % emptyCases.length);
    randomValue = gameCase[randomIndex];
}
// when we exit the while loop:
//     - randomValue would === ''
//     - randomIndex would point to its position in gameCase[]

方法2：使用第二個數組來跟蹤gameCase數組的哪些索引具有空值

var gameCase = ['', '', '', '', '', '', '', '', ''];
var emptyCases = [0,1,2,3,4,5,6,7,8];

if (emptyCases.length > 0) {
    // generate random Index from emptyCases[]
    var randomIndex = emptyCase[Math.round(Math.random()*emptyCase.length) % emptyCases.length];
    // get the corresponding value
    var randomValue = gameCase[randomIndex];
    // remove index from emptyCases[]
    emptyCases.splice(randomIndex, 1);
}

從某種意義上講，方法2更有效，因為您沒有浪費時間來生成/猜測隨機索引。 對於方法1，您需要一種方法來檢查gameCase[]是否還有任何空值，否則您可能會無限循環地永遠生成/猜測。

更多：在為gameCase[]設置值時，您需要相應地更新emptyCases[]以准確反映gameCase[]的狀態：

var gameCase = ['', '', '', '', '', '', '', '', ''];
var emptyCases = [0,1,2,3,4,5,6,7,8];

/* Update a value in gameCase[] at the specified index */
var setGameCaseValue = function(index, value) {
    // set value for gameCase[]
    gameCase[index] = value;

    if (value !== '') {    // we're setting a value
        // remove that index from emptyCases[]
        emptyCases.splice(emptyCases.indexOf(index), 1);   
    } else {    // we're setting it back to empty string
        // add that index into emptyCases[] that refers to the empty string in gameCase[]
        emptyCases.push(index);        
    }
};

setGameCaseValue(2, 'null');
// gameCase now has ['','','null','','','','','','']
// emptyCases now has [0,1,3,4,5,6,7,8]

setGameCaseValue(0, 'null');
// gameCase now has ['null','','null','','','','','','']
// emptyCases now has [1,3,4,5,6,7,8]

setGameCaseValue(5, 'null');
// gameCase now has ['null','','null','','','null','','','']
// emptyCases now has [1,3,4,6,7,8]

setGameCaseValue(7, 'null');
// gameCase now has ['null','','null','','','null','','null','']
// emptyCases now has [1,3,4,6,8]

請參閱小提琴： http : //jsfiddle.net/rWvnW/1/