学步园

/**<br /> * 该<span class='wp_keywordlink'><a href="http://www.xuebuyuan.com/category/%E7%AE%97%E6%B3%95" title="算法" target="_blank">算法</a></span>实现了大数+、-、x，但是没有实现对负数的处理，因为处理负数可以通过判断大小去规避这个问题。另外除法没有实现<br /> *<br /> * @author jie.xiang<br /> *<br /> */<br /> public class BigNumberCounter {<br /> public BigNumberCounter() {<br /> }<br /> /**<br /> * 当大数位数不相等的时候，往前面添加0，使其位数一致<br /> *<br /> * 对大数相减，不足即与前面借位。<br /> *<br /> * @param beforNum<br /> * @param afterNum<br /> * @return<br /> * @author jie.xiang<br /> */<br /> public String subNumbers(String beforNum, String afterNum) {<br /> int bLen = beforNum.length();<br /> int aLen = afterNum.length();<br /> int maxLength = Math.max(bLen, aLen);<br /> int distance = Math.abs(bLen - aLen);<br /> StringBuffer result = new StringBuffer();<br /> if (bLen > aLen) {<br /> afterNum = getZeroNumbers(distance) + afterNum;<br /> } else {<br /> beforNum = getZeroNumbers(distance) + beforNum;<br /> }<br /> int carry = 0;<br /> for (int i = maxLength - 1; i >= 0; i--) {<br /> int a = Integer.parseInt(beforNum.charAt(i) + "") - carry;<br /> int b = Integer.parseInt(afterNum.charAt(i) + "");<br /> carry = 0;<br /> if (a < b) {<br /> a += 10;<br /> carry = 1;<br /> if (i == 0) {<br /> result.append("-");<br /> }<br /> }<br /> result.append(String.valueOf(a - b));<br /> }<br /> return result.reverse().toString();<br /> }<br /> /**<br /> * 当大数位数不相等的时候，往前面添加0，使其位数一致<br /> *<br /> * 相加的值，与10产生的余数为结果，除以十位进位的内容。<br /> *<br /> * @param beforNum<br /> * @param afterNum<br /> * @return<br /> * @author jie.xiang<br /> */<br /> public String addNumbers(String beforNum, String afterNum) {<br /> int bLen = beforNum.length();<br /> int aLen = afterNum.length();<br /> int maxLength = Math.max(bLen, aLen);<br /> int distance = Math.abs(bLen - aLen);<br /> StringBuffer result = new StringBuffer();<br /> if (bLen > aLen) {<br /> afterNum = getZeroNumbers(distance) + afterNum;<br /> } else {<br /> beforNum = getZeroNumbers(distance) + beforNum;<br /> }<br /> int tempValue = 0;<br /> int carry = 0;<br /> for (int i = maxLength - 1; i >= 0; i--) {<br /> int a = Integer.parseInt(beforNum.charAt(i) + "");<br /> int b = Integer.parseInt(afterNum.charAt(i) + "");<br /> tempValue = a + b + carry;<br /> result.append(tempValue % 10);<br /> carry = tempValue / 10;<br /> }<br /> if (carry > 0) {<br /> result.append(carry);<br /> }<br /> return result.reverse().toString();<br /> }<br /> private String getCharNumbers(int length, String ch) {<br /> StringBuffer result = new StringBuffer();<br /> for (int i = 0; i < length; i++) {<br /> result.append(ch);<br /> }<br /> return result.toString();<br /> }<br /> private String getZeroNumbers(int length) {<br /> return getCharNumbers(length, "0");<br /> }<br /> /**<br /> * 大数相乘，逐位相乘，每个值与10产生的余数为结果，除以十位进位的内容，每次的值与前一位相乘的值相乘<br /> *<br /> * @param beforNum<br /> * @param afterNum<br /> * @return<br /> * @author jie.xiang<br /> */<br /> public String mutiNumbers(String beforNum, String afterNum) {<br /> int bLen = beforNum.length();<br /> int aLen = afterNum.length();<br /> int tempValue = 0;<br /> int carry = 0;<br /> String aNumber = "0";<br /> for (int i = aLen - 1; i >= 0; i--) {<br /> int a = Integer.parseInt(afterNum.charAt(i) + "");<br /> StringBuffer sb = new StringBuffer();<br /> String bNumber = "0";<br /> carry = 0;<br /> if (a == 0) {<br /> continue;<br /> }<br /> for (int j = bLen - 1; j >= 0; j--) {<br /> int b = Integer.parseInt(beforNum.charAt(j) + "");<br /> tempValue = a * b + carry;<br /> sb.append(tempValue % 10);<br /> carry = tempValue / 10;<br /> }<br /> if (carry > 0) {<br /> sb.append(carry);<br /> }<br /> bNumber = sb.reverse().toString() + getZeroNumbers(aLen - i - 1);<br /> bNumber = addNumbers(aNumber, bNumber);<br /> aNumber = bNumber;<br /> }<br /> return aNumber;<br /> }<br /> /**<br /> * 过滤结果，去除多余的0<br /> *<br /> * @param values<br /> * @return<br /> */<br /> private String getNoPrefixZero(String values) {<br /> String result = "";<br /> int i = 0;<br /> char zero = '0';<br /> for (; i < values.length(); i++) {<br /> if (values.charAt(i) != zero) {<br /> break;<br /> }<br /> }<br /> result += values.substring(i);<br /> if (result.length() == 0) {<br /> result = "0";<br /> }<br /> return result;<br /> }<br /> /**<br /> * @param args<br /> */<br /> public static void main(String[] args) {<br /> BigNumberCounter counter = new BigNumberCounter();<br /> System.out.println(counter.addNumbers(<br /> "99999999999999999999999999999999999999999999", "1"));<br /> System.out.println(counter.mutiNumbers("9999999999999999999999999",<br /> "9999999999999999999999999999999"));<br /> String value = counter.subNumbers(<br /> "25411111111111111111111111111111111111111136",<br /> "343453534546546757676856");<br /> System.out.println(counter.getNoPrefixZero(value));<br /> }<br /> }<br />

这几天突然被算法题难住了，确实忘记了哦，好久没做了，现在有时间自己再写写这些基本问题，基础不能忘啊，呵呵