Functions_bin_to_decimal.html

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var binStr = "11011010";

//算法一
function binToDecimal(bin){
	
	// 将二进制字符串分割成单数字字符数组
	var binStrArray = bin.split(''); // 1,1,0,1,1,0,1,0
	var decimal = 0; //保存十进制的最终结果
	var temp = 1; //临时保存每一位转换结果
	
	for (var i= binStrArray.length - 1, j = 0 ; i > 0 ; i-- , j++ ){ // i等于（二进制）2的幂，j是数组索引值

		// 从二进制数的最高有效位向最低有效位逐个迭代
		if(binStrArray[j] == 1){ // 如果第j个元素等于1，则需要计算i个2相乘（即2的i次幂）
			for (var k = i; k > 0 ; k-- ){ // 
				temp *= 2; 
			} 
			decimal += temp; //累加每一位的转换结果
			temp = 1; // 当前位转换完毕，重置临时变量
		}
	}
	alert(decimal);
}

//算法二
function binToDecimal2(bin){
	var decimal = 0, temp = 1, powerArray = [],pos=bin.indexOf('1');digits = bin.length;	
	
	//通过while循环得到二进制数值中所有1对应的幂的数组
	while (pos  > -1 ){ 
		powerArray.push(digits - pos - 1); //二进制数的位数减1再减索引值[7,6,4,3,1]
		pos = bin.indexOf('1', pos +1);
	}

	for (var i = 0; i < powerArray.length ; i++ ){
		var j =  powerArray[i];
		for (var k = 0; k<j ; k++ ){
			temp *= 2;
		}
		decimal += temp; temp = 1; 
	}
	alert(decimal);
}

//算法三：算法二的优化
function binToDecimal3(bin){
	var decimal = 0, temp = 1, pos=bin.indexOf('1');digits = bin.length;	
	
	//通过while循环得到二进制数值中所有1对应的幂的数组
	while (pos  > -1 ){ 
		var power = digits - pos - 1; //二进制数的位数减1再减索引值等于幂
		for (var i = 0; i < power ; i++ ){
				temp *= 2;
		}
		decimal += temp; temp = 1; 
		pos = bin.indexOf('1', pos +1);
	}
	alert(decimal);
}


//算法四
function binToDecimal4(bin){
	var decimal = 0, temp = 1, digits = bin.length; currentBit = bin.slice(0,1);
	while (digits > 0){
		if (currentBit == 1){
			var power = digits - 1; //二进制数的位数减1即等于幂
			for (var i = 0; i < power ; i++ ){
					temp *= 2;
			}
			decimal += temp; temp = 1; 		
		}
		bin = bin.slice(1); currentBit = bin.slice(0,1);digits = bin.length;
	}
	alert(decimal);
}

//算法五：算法四的变体——用数组代替字符串
function binToDecimal5(bin){
	var decimal = 0, temp = 1, binStrArray = bin.split(''),  currentBit = binStrArray.shift(), digits = binStrArray.length;;
	while (digits > 0){
		if (currentBit == 1){
			var power = digits; //数组长度即等于幂
			for (var i = 0; i < power ; i++ ){
					temp *= 2;
			}
			decimal += temp; temp = 1; 		
		}
		currentBit = binStrArray.shift(); digits = binStrArray.length;


	}
	alert(decimal);
}

//算法六：算法五的变体——使用pop()方法
function binToDecimal6(bin){
	var decimal = 0, temp = 1, binStrArray = bin.split(''),  currentBit = binStrArray.shift(), digits = binStrArray.length;;
	while (digits > 0){
		if (currentBit == 1){
			var power = digits; //数组长度即等于幂
			for (var i = 0; i < power ; i++ ){
					temp *= 2;
			}
			decimal += temp; temp = 1; 		
		}
		currentBit = binStrArray.shift(); digits = binStrArray.length;


	}
	alert(decimal);
}
 binToDecimal6(binStr); // 218

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