计ç®æ¶é´å¤æ度主è¦æ¯çè¿å 个ææ ï¼
1 input size(è¾å
¥)
2 basic operation/most costly operation(åºæ¬æä½)
3 determine average cases(å³å®æååå¹³åçæ¶é´)
4 sove it(计ç®)
å¨å泡æåºä¸çæ ¸å¿é¨åæ¯
for(i=0;i<n-1;i++)
for(j=0;j<n-1-i;j++)
if(a[j+1]<a[j]) swap(a[j],a[j+1]);
æ ¹æ®ä¸é¢çæ¥éª¤
1 size = n
2 basic operation = key comparison(æ¯è¾)
å 为æ¯è¾æ¯æ¯æ¬¡é½è¦åçï¼è交æ¢ä¸ä¸å®æ¯æ¬¡é½è¦å
3 average case = worst case
4 solve it
å°±æ¯è®¡ç®ä¸å
±è¿è¡å¤å°æ¬¡æ¯è¾è¿éå°±æ¯ç¨æ°å¦éçæ±åå
¬å¼sigmaæ±åºæ¥
æå
å±å¾ªç¯key comparisonç次æ°æ¯ä»0å°n-i-1ï¼å¤å±å¾ªç¯iä»0å°n-1
æ以æ»æ°æ¯å¯¹(n-1-i)æ±åï¼iä»0å°n-1
(n-1)*n - ï¼1+2+3+4+â¦+n-1ï¼= n(n-1)/2 = O(n^2)
æ以æ¶é´å¤æ度æ¯nçå¹³æ¹
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